DNA mutations in normal skin occur at high rates without cancerous growth. But when the skin’s architecture is broken down, those mutations can lead to cancer.Maintaing the skin’s architecture is critical to skin health.
Mutations Are Everywhere, But Cancer Isn’t
Scientists have looked at UV-exposed eyelid skin of middle-aged adults, and found that a square inch of normal, non-cancerous skin was riddled with mutations, many of them considered cancer drivers. The number of mutations in normal skin tissue rivaled the number seen in skin tumors, and exceeded the number of mutations seen in other tumor types, like breast cancer. Such findings once again set researchers’ expectations about how powerfully these mutations could promote cancer. There’s more to cancer than just mutations in our cells.
It’s The Architecture Stupid, Not the DNA
Prof. Dr. Cyrus Ghajar, Ph.D., a scientist at Fred Hutchinson Cancer Center, has noted that cancer-driving mutations are defined using animal studies. After identifying what is thought to be a common cancer-associated mutation in human cancers, researchers introduce the mutations into mice to see if tumors arise. If they do, they’re considered cancer drivers. But when you find these mutations in people in normal tissue, then what does that mean? It’s clearly not a driver. Mutations, it turns out, needs partners to drive cancer. They need another powerful mutation and an abnormal microenviornment, to induce cells toward cancerous growth.
The mutation-riddled reality of normal skin tissue prompts us to realize that skin has ways of handling mutations and keeping cellular growth normal. As Prof. Dr. Mina Bissell, Ph.D. at Berkeley has taught us, our organs are set up for function, and that function is inextricably linked to chemical envionment of the cells and the architecture into which the cells are embedded. Most cells in an organ are differentiated, meaning they perform a specialized function. And this differentiated state isn’t merely governed by an internal molecular decision-making process within each cell. It’s a collective process, a top-down process, where the architecture dictates function. If a cancer cell wanders into another organ and survives, it falls under the spell of the architecture, the top-down process instructing the cancer cell to renormalize. Dr. Bissell taught us this many years ago. As shes says, “to understand cancer it is important to understand that the phenotype can override the genotype.” Further, “influences such as what you eat, your internal metabolism, inflammation and the sun’s rays” affect your phenotype and hence your genotype. For example, in the aforementioned study of eyelids, the sun is causing mutations, but the phenotype, the cellular chemistry and architecture, has overridden the genotype, the mutated DNA, and the cells are behaving normally without cancerous growth.
Cancer Reverts if Normal Architecture is Restored
Dr. Bissell and team, in a landmark study, found that if they took breast cancer cells and put them back into a normal microenvionment, a normal architecture, then the cancer cells reverted back to normal. Their results demonstrated that the extracellular matrix, i.e the architecture and its inherent chemistry, dictate the phenotype of mammary epithelial cells, and thus in the model system tested, the tissue phenotype was dominant over the cellular genotype.
A Glimpse at the Big Picture of DNA, Cells, Architecture and Downward Causation
In the big picture, what I’m talking about is downward causation. The architecture instructs the pieces what to do. So the cellular structure is instructing what the DNA, all of the DNA, needs to do. That’s downward causation. We inherit downward causation because life derives from the cell. Cells make cells. Put DNA in a dish, it sits there, inert. Put DNA into a cell, it will begin to function, with that function dependent on what cell it is in. The cell, of course, has architecture, and it is the cell’s architecture that sets boundary conditions, instructing the molecules in the cell, including the molecules in the DNA, what they should do. We humans arise from cells, the mother’s egg – and that egg receives architectural signaling from the fathers sperm, which delivers DNA contained in it own architecture, the centriole. In other words, that cellular architecture and that of it’s surroundings, is critical to the cell’s function, to creating life, and whether cells will become cancerous. Along with Dr. Mina Bissell, Prof. Dr. Dennis Nobel, Ph.D., at Oxford, has been a pioneer in this way of thinking.
Sun Exposure Can Damage the Architecture, Not Just DNA
Concerning sun exposure and skin cancer, what happens when UV damages the skin? Is DNA damaged? Yes. But damaged too is the architecture, incuding the constiuent proteins and lipids in the architecture. As Drs. Bissell and Ghajar have taught us, it’s the cells surrounding architecture that will determine whether a cell becomes cancerous. So the UV damage of the proteins and lipids that make the architecture of the skin will be critical to determing whether the skin is cancerous or normal.
What to Do to Protect the Skin’s Architecture
What do you need to do for your skin to be healthy and free from cancer? Normalize the architecture of the skin. How do you do this? 1. First, dose your skin with sunlight in moderation to protect the skin’s architecture. If you’re out for long, wear a sunblock. 2. Eat well. Fruits and vegetables contain many of the nutrients to needed to maintain and regenerate the skin’s architecture. 3. You can also utilyze a skin care routine that maintains and regenerates the skin’s architecture. Using a combination of NeoGenesis Recovery and Barrier Renewal Cream, for example, will help to maintain and regenerate the architecture of the dermis and epidermis. NeoGenesis Recovery will also help to optimize the skin’s natural ability to repair DNA. Also available are retinoid products and antioxidant skin care products that can also help to prevent damage and rebuild the skin’s architecture.
Although plants and microorganisms such as algae possess some of the DNA damage response factors that are present in animal systems, they are missing many of the important regulators, such as the p53 tumor suppressor. The p53 mechanism halts the cell cycle when DNA damage is detected, giving repair machineries time to act. These observations point to the differences in the DNA damage response mechanisms between plants and animals. While DNA repair enzymes from plants may help the skin when topically applied, optimizing the DNA repair mechanisms inherent in animals is the optimal strategy for repairing DNA in animals.Adipose mesenchymal stem cell released molecules (secretome) help to optimize inherent DNA repair mechanisms when topically applied to the skin, including heat shock proteins.More importantly, the molecules help to rebuild the architecture of the skin, which prevents mutations from forming cancerous cells (see my Blog on this topic).
All plant extract contain DNA repair enzymes
If you’re using a product with plant extract, you’re likely using DNA repair enzymes. All, or nearly all, plants contain DNA repair enzymes. Keep in mind, this is important, an intrinsic feature of plant and microorganism DNA repair pathways is that they are not error-free, leading to potentially transmissible mutational alterations. The error-prone nature of some DNA repair mechanisms, however, increases the genetic diversity and variability of the populations, thus contributing to the evolution of plant genomes. In other words, despite the recent hype about DNA repair enzymes in plants/microorganisms, they don’t work well and are “error prone.”
Animals have more robust DNA reair enzymes than do plants
This is not true in animals. They are not error prone. Because animals must better protect their DNA than do plants to prevent and repair mutations that are harmeful, potentially lethal. This is why stem cells in the skin faciltate DNA repair as only animals can do.
Stem cells in the skin have the most robust DNA repair mechanisms
As stated in a presitigious scientific journal, Molecular Cell, ” adult stem cells are endowed with a superior capacity to prevent the accumulation of genetic lesions, repair them, or avoid their propagation to daughter cells, which would be particularly detrimental to the whole organism.” Further stated, “SCs [stem cells] count upon robust antioxidant defenses (which limit genotoxicity) and a superior DDR (to repair unavoidable damage). These mechanisms are in place to protect cellular homeostasis.”
DNA repair mechanisms: it’s complicated and very efficient if enabled
DNA double strand breaks (DSBs) are a serious threat to genome stability and the erroneous repair of DNA may lead to chromosomal rearrangements with potentially lethal consequences, including cancer, for an organism. The response to DSBs elicits a highly complex and organized cellular program, called the DNA damage response (DDR), setting in motion processes that mitigate the adverse effects of DNA damage and facilitate DNA repair. Broken DNA is usually repaired by two mechanistically distinct pathways: homologous recombination (HR) and non-homologous end joining (NHEJ). HR is a complex, multistep process that allows large sections of DNA to move from one chromosome to another. NHEJ is a DNA repair mechanism that fuses broken DNA ends together without the need for a homologous template While HR uses a homologous DNA strand as a template for error-free repair, NHEJ is inherently error-prone and does not rely on sequence homology. The preferred mode of repair and cellular consequences of DDR varies between organisms and is also dependant on cell type and cell cycle context. For example, while HR is the preferred mode of repair in many unicellular organisms such as budding and fission yeast, NHEJ is the prevalent pathway in plants and animals.
Plants versus animals, digging deeper into the mechanisms
However, in many aspects, plants respond differently to DNA insults than do animals. The constant risk of tumor formation in animals has led to evolution of DDR that assures precise genome maintenance, often resulting in apoptotic death of significantly damaged cells. The lack of such a strong selective constraint presumably permitted evolution of a less potent DDR in plants, making plants more prone to genome damage. Furthermore, plant cells are exposed to high levels of genotoxic stress resulting from long-term exposure to solar ultraviolet (UV) irradiation, photosynthesis and extended periods of desiccation. Thus, some features of plant DDR and DSB repair may deviate from models primarily established from studies in yeasts and mammals.
DNA repair in animals is even more complicated than that described by the two major pathways. Five DNA repair mechanisms are usually distinguished: (a) direct DNA damage reversal, (b) BER, (c) mismatch repair (MMR), (d) nucleotide excision repair (NER), and (e) homologous recombination (HR) and non-homologous end joining (NHEJ). DNA repair pathways were originally restricted to the nuclear compartment. Ample evidence indicates that mitochondria possess a number of DNA repair factors and mechanisms shared with the nuclear processes.
From: Sottile and Nadin (2018). Sources of DNA damage and repair mechanisms. Endogenous and exogenous agents constantly impact on DNA. They may cause many different forms of DNA damage. The scheme shows the five major DNA repair mechanisms operating in the nucleus of mammalian cells capable of removing a wide range of DNA lesions: direct damage reversal, base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), homologous recombination (HR), and non-homologous end joining (NHEJ). The BER system may also be found in the mitochondria. ROS reactive oxygen species, IR ionizing radiation, TOPOII topoisomerase II
Not included in the above summary is a new form of DNA repair in animals, called neucleophagy. This was just reported in October 2024 by a group of scientists at Oxford. Found to be evolutionarily conserved and clinically relevant, we’ll know more baout this mechanism in the coming years. Its mediated by TEX264, an intrinsically disordered protein, and as such, I suspect this will be an important and widespread DNA repair mechanism, possibly involving adult stem cells and their secretome – stay tuned.
How adult adipose mesenchymal stem cell scretome faciltates DNA repair
These complicated processes are faciltated by a number of molecules, including proteins, such as heat shock proteins, released by adipose mesenchymal stem cells (ADSCs). Another example, ADSCs release sirtuins, which are involved in DNA repair. The sirtuins work both as protein activators and chromatin-structure-modifying enzymes. Deacetylation carried by sirtuins represents a basic epigenetic mechanism. Histone modifications including deacetylation and poly-(ADP)-ribosylation compromise an essential part of physiological ageing processes that are involved in the pathogenesis of ageing-related diseases. Stem cells are also known to produce 5-hydroxymethylcytosine binding, embryonic stem-cell-specific (HMCES) protein functions as an intermediate in DNA interstrand cross-link repair, part of BER. Antioxidants from ADSCs are also important for DNA repair. They include: Superoxide dismutase (SOD): This enzyme converts superoxide radicals (O2-) into hydrogen peroxide (H2O2), which is then further broken down by other enzymes like catalase. Catalase (CAT): Catalase directly breaks down hydrogen peroxide (H2O2) into water and oxygen, preventing further oxidative damage to cellular components including DNA. Peroxiredoxins (Prxs): This family of enzymes also plays a significant role in scavenging reactive oxygen species, particularly in the nucleus where DNA is located, and can directly contribute to DNA repair mechanisms.
The secretome from ADSCs was tested for skin repair following irradiation, where DNA and protein damage is a key component in the radiation dermatitis. Working with Dr, Michael Traub, N.D., NeoGeneis found that simple topical application of ADSC secretome in its Recovery product significantly reduced radiation dermatitis. The Recovery works through the many types of molecules found in the ADSC (and fibroblast) secretome that enable the skin’s robust DNA repair mechanisms to work optimally.
Beyond the hype of plant/microorganism DNA repair enzymes
You can see that using the secretome from ADSCs is much more powerful than using a plant or microorganism extract to repair DNA. While DNA repair enzymes from plants and microorganisms have been found to reduce cyclobutane pyrimidine dimers, and presumably repair DNA in humans when compared to doing nothing, the “DNA repair” products on the market contain many other ingredients that are at least partially responsible for their efficacy. Those other ingredients include antioxidants and sunblocks. If you want a great topical product to repair DNA in your skin cells, use NeoGenesis Recovery that is full of the molecules released from ADSCs, including those molecules in exosomes and those molecules in the soluble fraction.
NeoGenesis uses Hydroxypinacolone retinoate (HPR), a newer retinoid that is less irritating than tretinoin and has been found to be as effective in vitro at promoting collagen production. HPR is also more stable than other retinoids in the presence of sunlight and air. Unlike retinol, HPR directly binds to the retinoid receptors and is therefore more effective and less irritating than retinol. The efficacy of HPR is similar to retinoic acid. However retinoic acid (tretinoin) can cause significant irritation of the skin, and is available only by a physician’s prescription. Retinoids can provide great benefit to aging skin. In this blog, I’ll explore some of the mechanisms by which retinoids benefit both the epidermis and the dermis. (Christine Preston contributed to this blog).
From Quan (2023)Epidermal and dermal aging of human skin. Skin aging includes the thinning of both the epidermis and dermis.
Over time, many alterations occur within the epidermis, collectively known as epidermal aging. These changes in time are characterized by the thinning of the epidermal layer and the flattening of rete ridges (as depicted in Fig 1, on the right). Rete ridges (RR) form an interdigitated surface area that reinforces cohesion between the epidermis and dermis, and this structure demonstrates plasticity, responding dynamically to stimuli such as UV irradiation. RR adapts to disruptions of its boundary during wound repair when cells lose hyper-adhesiveness, allowing the skin to appropriately remodel itself. The principal cause of epidermal aging can be traced to a reduction in the proliferation and turnover of keratinocytes, linked partially to the depletion of interfollicular epidermal (IFE) stem cells and dysfunctional Rete Ridges, leading to poor healing and thinning of the epidermis.
Collagen type, COL17A1 has been of particular interest due to its role in maintaining the homeostasis of the skin stem cells. COL17A1 is a structural element within the dermal–epidermal basement membrane, and it is synthesized by epidermal keratinocytes, not fibroblasts (Xiang et al, 2022). COL17A1 is primarily expressed in the uppermost extensions of the rete ridges area, where the niches for IFE stem cells are located. Research results have suggested a reduction in the expression of COL17A1 in human skin affected by both intrinsic and extrinsic aging factors, including human skin exposed to acute UV irradiation. The decrease in COL17A1 levels within the area specific to the rete ridges can reduce the adherence of IFE stem cells to their designated locations, leading to their removal from the skin. Consequently, the reduction of collagen protein, COL17A1, results in decreased rates of keratinocyte renewal and the development of thinner epidermal layers, the primary morphological characteristic of aging skin.
Human skin has developed two main defense mechanisms to guard against the damaging effects of UV: 1. epidermal thickening, 2. and the stimulation of melanin synthesis, however, photoprotection through increased melanogenesis is more important. As we think about retinoids and what they do for the skin, think about how retinoids help to maintain the normal structure of the skin, can actually thicken the epidermis and dermis, and how important this is for skin function and protection, including protection against UV.
Retinoids, which refer to a group of vitamin A derivatives, are among the most-extensively studied ingredients in skincare for combatting aging and enhancing the appearance of mature skin. Retinoids can stimulate collagen synthesis, inhibit MMP (Matrix metalloproteinases – too much of this activity can break-down proteinaceous tissues) activity, reduce oxidative stress, and modulate gene expression (Quan, 2023). Retinoids have exhibited efficacy in ameliorating the visual manifestations of both intrinsic and extrinsic aging, such as wrinkles, fine lines, and irregular pigmentation. The mechanisms of retinoid’s action may involve the activation of retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which regulate gene transcription and cell differentiation. Retinoids may also modulate the activity of growth factors and cytokines involved in ECM turnover and inflammation. Retinoic acid (RA) is the active form of vitamin A and its precursor is called retinol (ROL). ROL can be converted into its active metabolite within human skin. When retinol is applied topically to human skin, it can penetrate the skin and undergo sequential conversion to retinaldehyde and then to retinoic acid
Skin-equivalent cultures have been used to investigate the regulatory role of retinoids in collagen homeostasis. Typically, these simplified skin constructs feature stratified and differentiated keratinocytes, representing the epidermal layer, layered atop a collagen lattice primarily comprising Type I collagen. Dermal fibroblasts are embedded within this lattice to mimic the dermal layer. When subjected to retinoic acid treatment, these skin-equivalent cultures exhibit a thickened epidermis with a substantial increase in the number of keratinocyte layers and elicit a dermal response akin to the effects observed when retinoic acid is topically applied to human skin in vivo. Consequently, skin-equivalent cultures hold significant potential as a valuable model for delving into the mechanisms by which retinoids enhance the appearance of aging skin in humans.
Increasing the Thickness of the Epidermis and the Vascularity of the Dermis in Aged Human Skin In Vivo Using Topical Retinoids: Stimulating the Growth of Epidermal Keratinocytes and Dermal Endothelial Cells
Topical application of retinoids to aged human skin in a live setting has been found to significantly enhance the thickness of the epidermis by stimulating the proliferation of epidermal keratinocytes, and increasing the number of Rete Ridges. In addition to improving epidermal thickness, topical retinoid has shown a notable increase in the proliferation of endothelial cells and blood vessels in the papillary dermis. These findings suggest that the topical application of retinoids results in the thickening of the epidermal layer and the development of fresh blood vessels within the dermis. The AP-1 transcription factor is critical to enabling the proliferation of keratinocytes in response to growth factors, cytokines, and various stimuli. The AP-1 complex consists of c-Jun and c-Fos, and it has been observed that topical retinoids significantly increases the expression of the epidermal-specific c-Jun protein, leading to a substantial increase in epidermal thickness. There is also evidence that the expression of c-Fos protein increases with retinoid treatment. These findings suggest that topical retinoids enhance the activity of the epidermal-specific c-Jun, and possibly c-Fos transcription factors, thereby stimulating the proliferation of epidermal keratinocytes in aged human skin in vivo.
Topical Retinoids Improve the Dermal ECM Microenvironment by Promoting the Production of Collagenous ECM in Aged Human Skin In Vivo
Topical retinoid treatment increases Type I collagen expression, which constitutes 80–85% of the dermal ECM, while collagen type III constitutes about 8–11%. Topical retinoid also significantly enhances the expression of fibronectin and tropoelastin. In aged human skin in vivo, topical retinoid effectively activates dermal fibroblasts, leading to the substantial production of collagenous ECM through the activation of the TGF-β/Smad pathway, which is a key regulator of ECM production. Topical retinoid administration causes a significant increase in TGF-β1 mRNA expression and a decrease in inhibitory Smad7, while other components of the TGF-β pathway remain unaffected. Additionally, topical retinoid leads to an increase in the expression of connective tissue growth factor (CTGF/CCN2), which is substantially reduced in the dermis of aged individuals and contributes to the decline in collagen production associated with aging. These findings provide evidence that topical retinoid stimulates the production of ECM by dermal fibroblasts through the upregulation of the TGF-β/CTGF pathway in aged human skin.
In addition to the upregulation of TGF-β/CTGF pathway, retinoic acid significantly reduces CCN1 gene expression in both naturally aged and photoaged human skin in vivo. CCN1 is a negative regulator of collagen homeostasis by inhibiting the TGF-β/CTGF pathway and stimulating MMPs’ induction. These data suggest that the mechanism by which topical ROL improves aged skin, through increased collagen production and inhibition of MMPs, may involve the downregulation of CCN1. Thus, retinoids are acting through multiple pathways, inhibiting some and activating others.
In aging skin, decreased vascularity and thinning of the dermis and epidermis are substantial factors contributing to skin fragility and hindered wound healing. Blood flow to the skin, the largest organ in the body, is reduced by 40% between the ages of 20 to 70 years. Topical retinoids not only enhances ECM production, but also improves the dermal microenvironment by promoting the expansion of vasculature through endothelial cell proliferation in aged human skin. An age-related reduction in cutaneous vasculature has been reported. The increased vascularity of the dermis induced by topical retinoids can improve skin blood flow and create a more-favorable microenvironment for the homeostasis of the epidermis and dermis. Further, the promotion of epidermal keratinocyte proliferation and the restoration of ECM production by topical retinoid could create a supportive environment for the growth of endothelial cells and the development of dermal blood vessels. Epidermal keratinocytes are a significant source of vascular endothelial growth factor (VEGF), a powerful factor in promoting angiogenesis. Furthermore, increased production of dermal ECM has been demonstrated to stimulate the proliferation of endothelial cells. As a result, the augmented dermal vascularity facilitated by retinoids may have a significant impact on the homeostasis of both the epidermis and dermis.
Hydroxypinacolone Retinoate (HPR) for Anti-Aging, Photodamage, and Acne
Hydroxypinacolone retinoate (HPR) has demonstrated positive effects as a topical anti-aging ingredient, the authors of the study writing, “Together these data suggest that HPR is an effective alternative to ATRA and other less potent retinoids in the treatment of aging skin without the detrimental side-effects. And the combination of retinoids and salicylic acid can be used to ameliorate the signs of photoaging.
Data have confirmed past studies indicating that topical retinoids are under-used for acne. Further, HPR has been successfully used to treat comedonal-papular, mild to moderate acne of the face. In this study, papain was also used, in addition to HPR, as an exfoliant, and in many cases acne patients may benefit from combination therapies, such as the use of retinoids (HPR) with salicylic acid to better treat acne.
Carotenoids, Like Beta-Carotene, Convert to Retinoids When Topically Applied
You’ll notice on the label of NeoGenesis Skin Restore Serum, that in addition to HPR, carotenoids, including beta-carotene, are included in the product. While topically applied carotenoids absorb into the skin and are converted to retinoids in the skin, the carotenoids also provide antioxidant benefit to the skin. The beautiful yellow color of the vitamin A product, Skin Restore Serum, reflects the yellow pigmented carotenoid antioxidants loaded into the serum.
The amount of carotenoids in the skin depends on dietary intake, and their bioavailability from various foods, with fruits and vegetables as an important source.. After absorption in the gut and transportation into the skin, carotenoids accumulate in the skin, including the adipocytes in the hypodermis. The skin protective benefits of carotenoids, especially from those residing in the epidermis, are many, including protection from UV and air pollution.
Retinoids and Photosensitivity
Photosensitivity to retinoids appears to be a rare event, and quite to the contrary, retinoids have been found to successfully treat some forms of skin photosensitivity. First, let’s dispel the somewhat common belief that topical retinoids enhance UV-induced inflammation. Smit et al (1999) evaluated the minimal erythema dose (MED) for UVB irradiation on topical all-trans RA (tretinoin cream 0.05%) pre-treated skin compared with vehicle cream pre-treated skin and untreated skin. Their study found no significant difference for the MED values either 24 or 48 h after UVB irradiation between the all-trans RA cream treated skin, and the vehicle cream treated skin and untreated skin. In other words, topical retinoid caused no enhanced inflammation when the skin is exposed to UV.
Second, Actinic folliculitis (AF) is a rare recurrent seasonal photodermatosis, relatively newly characterized by nonpruritic, monomorphic pustules and papules appearing 4-24 h after exposure to sunlight. Lesions usually affect the face but also appear on the upper chest and arms. Resolution normally occurs within 7-10 days with cessation of sunlight exposure. AF is resistant to standard treatments used for acne vulgaris and acne rosacea, with only oral retinoids previously being reported as effective. Academic dermatologists in the UK have reported that AF responding extremely effectively to a topical retinoid.
Discussing photosensitivity, be clear that HPA is relatively stable in light and in the air. Applying and using HPA in normal lighting conditions will not degrade the product.
Long Term andOveruse of Retinoids
While a significantly higher concentration of retinol (0.4%) is required to attain similar outcomes as observed with topical retinoic acid, retinol triggers similar histological alterations (epidermal thickening and dermal ECM production) as retinoic acid. However, inappropriate or excessive use of topical retinoids or retinoic acid may also result in potential side effects. These commonly include skin dryness, redness, and peeling, which can cause discomfort. However, these side effects typically diminish over time as the skin adjusts to the product. Evidence suggests that HPR will induce fewer adverse side-effects than the other retinoids.
Long-term use of retinoids (studied for up to 2 years) have found beneficial effects to the skin throughout the treatment period, and a good safety profile. While most of the benefit is seen within 6 months following onset of the treatment, long term use can maintain the positive effects.
Summary
Topical retinoids (TR) are a safe and effective addition to one’s skin care routine, especially for aged skin. TR provides major benefits to the skin, including increased thickness of the epidermis and dermis, and enhanced blood flow to the skin. There are few side effects of retinoids, and if chosen properly, retinoid products, such as those that use HPR, are well tolerated by those with sensitive skin. Photosensitivity is not an issue, and their use with vitamin C/antioxidant products, such as those using gentle liposomal vitamin C (liposomal ascorbic acid), provides extra benefit.
Dr. Greg Maguire's Skin Care 