Tretinoin: Does It Really Cause Sun Sensitivity?

Anyone who has used tretinoin before remembers the instructions: apply a pea-sized amount at night. It’s true, tretinoin should be applied at night, but it might not be why you think.  Many believe it is because it causes sensitivity to the sun. So, you want to apply it when the sun isn’t out, right? But the impact of tretinoin on the skin is long lasting (see post, Myth: You Need to Apply Tretinoin Every Night), so the increased sensitivity to sun will still be present in the morning after you apply it, throughout the day, and even days to weeks after stopping its use! 

Why Apply Tretinoin at Night?

The primary reason for applying tretinoin at night is to prevent its photodegradation—the breakdown of the compound when exposed to ultraviolet light. Research indicates that tretinoin is particularly sensitive to ultraviolet A (UVA) light, which causes it to degrade and lose effectiveness (Tashtoush et al., 2008).

Why Does Tretinoin Cause Sun Sensitivity?

Paradoxically, tretinoin can both protect from, and make the skin more sensitive to, the sun. Sensitivity to sun is primarily the result of the long-term effects of tretinoin on the skin, which persist throughout the day not only after application.

Mechanisms Increasing Sun Sensitivity

• Thinning of the Stratum Corneum: The stratum corneum is the outermost layer of skin made up of dead skin cells and natural oils (lipids) that act like glue to keep it all together. It is an extremely important layer that has many functions including retention of moisture and acting as a natural barrier against environmental stressors, including ultraviolet radiation (sunlight). Tretinoin accelerates epidermal turnover (epidermal hyperplasia), which results in a thinner, more compact stratum corneum. Although this improves skin texture, it also reduces protection against UV exposure, increasing the risk of sunburn (Griffiths et al., 1993).

  

  The stratum corneum is the outermost layer of skin made up of dead skin cells and natural oils (lipids) that acts like glue to keep it all together.

• Increased UV-Induced Collagen Degradation: While tretinoin is renowned for promoting collagen preservation and synthesis, its initial use can temporarily make the skin more vulnerable to collagen breakdown. UV exposure quickly upregulates matrix metalloproteinases (MMPs), the enzymes responsible for degrading collagen. Early on, tretinoin amplifies this process leading to heightened short-term sensitivity to UV-induced collagen degradation. (Fisher et al., 1997).

• Alterations in Epidermal Cell Structure: Tretinoin modifies epidermal differentiation (how the cells grow from baby to adult cells) and changes the carbohydrate structures on the skin’s surface. These alterations lead to differences in skin hydration and cellular responses to environmental stress. In effect, the skin begins to resemble mucosal surfaces (like that of the lips), which are inherently more sensitive to external stimuli, including ultraviolet light, contributing to increased inflammation and photosensitivity (Griffiths et al., 1996).

• Enhanced Erythema and Inflammatory Response: By increasing the release of inflammatory mediators, tretinoin heightens the skin’s sensitivity to UV-induced erythema (redness). As a result, even minimal sun exposure can trigger significant inflammation and visible redness compared to untreated skin (Fisher et al., 1996).

  
  

Mechanisms that Counteract Sun Damage

• Stimulates Collagen Production & Repairs UV Damage: Over time, tretinoin reverses photodamage by increasing collagen synthesis and reducing fine lines and wrinkles. Research has demonstrated that tretinoin improves dermal structure and enhances skin repair from sun-induced damage​ (Griffiths et al. 1993).

• Reduces Chronic UV-Induced MMP Activity: While tretinoin initially does not prevent acute UV-induced matrix metalloproteinase (MMP) activity, long-term use suppresses chronic MMP upregulation, making the skin more resistant to collagen breakdown and premature aging (Fisher et al., 1997)​.

How to Protect Your Skin While Using Tretinoin

Since tretinoin increases sun sensitivity through several mechanisms, proper sun protection is essential. Protecting yourself adequately from the sun during tretinoin application will maximize the benefit and limit the potential harms of tretinoin use. Consider the following precautions:

• Limit Facial Sun Exposure: Avoid prolonged direct sunlight, especially between 10 AM and 4 PM. Wear protective clothing like hats and visors. (Sensible amounts of sun-exposure to the rest of the skin can be an important source of vitamin D)

• Apply Broad-Spectrum Sunscreen: Use sunscreen when sun exposure cannot be consumed responsibily.

• Avoid Harsh Products: Steer clear of harsh cleansers, astringents, toners, or peels that may strip away the already-thinned stratum corneum.

• Help Your Barrier: If still experiencing mild dryness or irritation, try a bland facial moisturizer to help repair and strengthen the stratum corneum. If you are still getting dryness and irritation, tretinoin may not agree with your skin. It's ok, its not for everyone and you can still have great skin!

Dr. Ryan M. Trowbridge, MD, MS, MA

Harvard-Trained, Board-Certified Dermatologist and DermMythBuster

P.S. Have you come across any new or conflicting research on this topic? Please share—I’d love to explore it further with you!

Would you like to try tretinoin? You can obtain an online consultation from Dr. Trowbridge at Bridge Dermatology if you currently reside in California, Connecticut, Illinois, or Nebraska.

Citations

• Fisher, G. J., Datta, S. C., Talwar, H. S., et al. (1996). Molecular basis of sun-induced premature skin aging and retinoid antagonism. Nature, 379, 335–339.

• Fisher, G. J., Wang, Z. Q., Datta, S. C., et al. (1997). Pathophysiology of premature skin aging induced by ultraviolet light. New England Journal of Medicine, 337, 1419–1428.

• Griffiths, C. E. M., Russman, A., Majmudar, G., et al. (1993). Restoration of collagen formation in photodamaged human skin by tretinoin (retinoic acid). New England Journal of Medicine, 329, 530–535.

• Griffiths, C. E. M., Dabelsteen, E., & Voorhees, J. J. (1996). Topical retinoic acid changes the epidermal cell surface glycosylation pattern towards that of a mucosal epithelium. British Journal of Dermatology, 134, 431–436.

• Tashtoush, B. M., Jacobson, E. L., & Jacobson, M. K. (2008). UVA is the major contributor to the photodegradation of tretinoin and isotretinoin: Implications for development of improved pharmaceutical formulations. International Journal of Pharmaceutics, 352(1–2), 123–128. doi:10.1016/j.ijpharm.2007.10.045