UV Radiation: How Sun Exposure Ages and Harms Your Skin
By Clarissa Portocarrero
Reviewed by Dr. Nicole Joy
What Is UV Radiation and Why Is It Harmful?
Ultraviolet radiation (UVR) from the sun is a major cause of premature skin aging, known as photoaging, and significantly increases the risk of skin cancer. While many think of sun damage as only sunburns, UVR affects skin at a cellular level long before visible damage appears.
UVA vs. UVB: Different Rays, Different Risks
UVA rays have a longer wavelength than UVB and make up about 90–95% of the UV radiation that reaches your skin. This means that UVA penetrates deeper, reaching the dermis, which is the layer of skin that gives it structure and strength through collagen and elastin. Once inside, UVA rays create harmful molecules called reactive oxygen species (ROS) that can damage important parts of your skin, like proteins, fats, and DNA. This damage triggers enzymes that break down collagen and elastin, leading to wrinkles, sagging, and rough skin texture over time. UVA also causes long-term pigmentation changes and plays a role in skin aging and skin cancer by creating ongoing damage and making it harder for your skin to repair itself. Unlike UVB, UVA can pass through glass and stays fairly constant throughout the day and year. That’s why it’s so important to use a broad-spectrum sunscreen that protects against both UVA and UVB rays.
UVB rays have a shorter wavelength and make up only about 5% of the UV radiation that reaches your skin. However, UVB rays are more powerful when it comes to causing damage. They mostly affect the top layer of the skin, called the epidermis, where they directly damage the DNA in your skin cells. Over time, this can lead to mutations that affect how cells grow and repair, increasing the risk of skin cancers like melanoma. UVB is also the main cause of sunburn, leading to redness, pain, and inflammation. Unlike UVA, UVB levels change throughout the day and year, peaking around midday and being strongest in the summer. Protection against UVB is measured by the Sun Protection Factor (SPF) indicated on sunscreen labels.
The Visible Effects of Photoaging
Cumulative UVR exposure over years leads to structural and functional changes in the skin known as photoaging, or sun-related skin aging. Visible signs include:
· Fine and coarse wrinkles (rhytides)
· Rough, dry skin texture (xerosis or elastosis)
· Thinning or thickening of the skin (epidermal atrophy or hyperplasia)
· Uneven skin tone with dark patches (mottled hyperpigmentation, solar lentigines)
· Yellowish discoloration due to abnormal elastin buildup (actinic elastosis)
· Visible, dilated blood vessels (telangiectasias)
· Enlarged pores and uneven surface (cutaneous roughness)
· Sagging or loose skin (skin laxity)
· Precancerous scaly lesions (actinic keratoses)
· Fragile skin that bruises easily (actinic purpura)
· Deep furrows and leathery appearance on sun-exposed areas (cutis rhomboidalis nuchae)
The Link Between Sun Damage and Skin Cancer
Ultraviolet radiation (UVR) is the primary environmental cause of most skin cancers. It contributes to both direct DNA mutations and indirect oxidative damage that impair the body’s ability to repair cells and control abnormal growth. Chronic exposure, particularly without adequate sun protection, increases the risk for a spectrum of skin malignancies:
Actinic keratoses (AKs): These are precancerous lesions that appear as rough, scaly patches on sun-exposed areas such as the face, scalp, forearms, and hands. AKs result from long-term UVR-induced damage to keratinocytes and represent an early step in the progression to squamous cell carcinoma. Although not all AKs become cancerous, their presence signals significant sun damage and require regular monitoring and management.
Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC): Basal cell carcinoma and squamous cell carcinoma are the two most common types of skin cancer. They develop in skin cells called keratinocytes, which make up most of the outer layer of your skin. These cancers are mainly caused by long-term sun exposure, especially in fair-skinned individuals who spend a lot of time outdoors without proper sun protection. Over time, UVR can damage the DNA in these cells, leading to abnormal growth and skin cancer.
Melanoma: This is the most aggressive form of skin cancer and is strongly associated with intermittent, intense UVB exposure, particularly episodes that cause blistering sunburns during childhood and adolescence. UVB-induced DNA mutations in melanocytes—pigment-producing skin cells—which may trigger changes that cause these skin cells to grow out of control. While less common than other skin cancers, melanoma carries a high risk of metastasis if not detected early.
Daily Protection is Essential
UVA rays are present year-round, can penetrate clouds, and even pass through glass—meaning your skin is exposed whether you’re indoors by a window or driving in your car. That’s why sunscreen isn’t just for beach days. Daily application is key to preventing long-term sun damage.
Want to learn how to choose the right sunscreen? Stay tuned for our upcoming article, where we break down active ingredients, explain what to look for on labels, and debunk common sunscreen myths to help you protect your skin with confidence.
References
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Battie C, et al. New insights in photoaging, UVA induced damage and skin types. Exp Dermatol. 2014;23(Suppl 1):7–12. doi:10.1111/exd.12388
Matsumura Y, Ananthaswamy HN. Toxic effects of ultraviolet radiation on the skin. Toxicol Appl Pharmacol.2004;195(3):298–308. doi:10.1016/j.taap.2003.08.019
Chien AL, Kang S. Photoaging. UpToDate. Sections on clinical features and pathogenesis. Literature review current through April 2025.
