What is the UV spectrum and why is it all important?
Sunlight is not just heat. Its spectrum is very broad: although UV (ultraviolet) constitutes a very small part of it, this part creates the most important photobiological consequences for the skin. It has three main groups: UVA (320–400 nm), UVB (290–320 nm), and UVC (200–290 nm). UVC is largely blocked by the ozone layer; it is UVA and UVB that truly concern the skin on the ground.
UVB stays on the surface; it is at the center of burns, redness, and DNA damage. UVA, on the other hand, penetrates deeper; it reaches the dermis, causes elastin-collagen damage, and is the main source of long-term photoaging and increased pigmentation. Even on a cloudy day, a large part of the UVA load continues.
Visible light and infrared: the new generation photothreat
Studies conducted in the last 10 years have shown that not only UV but also HEVL (high-energy visible light) and IR-A (infrared) are significant for photoaging and especially for hyperpigmentation in darker skin types. For this reason, the importance of sunscreens that protect not only against UVA/UVB but also contain mineral (zinc oxide, titanium dioxide) and pigmented components has increased.
In patients with melasma and a tendency for spots, chemical filters alone may not be sufficient. Further in this section, the selection of the correct sunscreen will be discussed as a separate topic; here we focus on understanding the biological background.
UV dose and timing
The UV index (UVI) varies by time of day, geography, and season. In Turkey, between 11:00 and 16:00 in June-August, the UVI usually rises to the 8-10 range; this is the "very high" and "extreme" band. During these hours, sun protection is not just an aesthetic but a medical necessity.
Most of my patients say, "I don't get burned." However, in patients with darker skin tones, UVA damage is cumulative; even doses that do not cause burns trigger collagen damage and pigment accumulation. Sun exposure is not a matter of "feeling," but a matter of accumulation.
- Between 11:00 and 16:00, UV is at its peak in Turkey.
- A cloudy day transmits up to 70% of UVA.
- Water and sand can increase the UV load by 20-80% through reflection.
- Glass windows block UVB but transmit UVA; damage occurs even during driving.
- Shade reduces the total dose but does not eliminate UV.
Clinical note:I often see in patient follow-ups: patients who say "I don't stay on the beach anyway" have intense signs of photoaging on their hands, neck V-area, and forehead. The reason for this is daily, unconscious, accumulated UV exposure.
Effects of UV exposure on the skin
In the short term, burns, redness, and acute inflammation are observed. In the medium term, tanning is actually a defense response; it is the skin's response to DNA damage. In the long term, collagen loss, elastosis, solar lentigo (age spots), actinic keratosis, and skin cancers come into play.
According to data from the American Academy of Dermatology, 80-90% of age-related skin changes are not chronological but photographic, meaning UV-induced. In other words, a large part of what is called aging is actually sun damage. This information makes sunscreen a health tool, not a luxury.
Vitamin D paradox: is the sun good or bad?
Patients often ask: "If UV is so harmful, what about vitamin D?" This is an important question. The truth is: a few minutes of controlled UVB exposure to the skin is sufficient for vitamin D synthesis. A few minutes on the arms and legs, 2-3 days a week, outside of peak UVI, is sufficient for most healthy individuals.
In patients with a tendency for spots, melasma, or a history of skin cancer, trying to get vitamin D from the sun is not logical in terms of risk-benefit; vitamin D can be supplemented orally and blood levels monitored. The argument that sunscreen blocks vitamin D has largely become invalid in current literature.
Attention:Sunburn is not a punishment, but an emergency signal from the skin. Subjecting burned skin to aggressive treatments (peeling, laser, retinoid) in the next 48 hours is risky and wrong.
Four layers of photoprotection
Modern photoprotection is not just about applying cream. I advocate a four-layered approach: behavioral (avoiding peak hours), physical (UV-protective clothing, wide-brimmed hat, UV glasses), topical (sunscreen), and systemic (antioxidant support, nutrition).
Effective protection begins when these four layers work together. Relying solely on sunscreen is not practically sufficient; because most patients do not apply enough, the actual SPF remains very low. In the following sections, I will explain the correct application logic in great detail.
Skin cancer and regular examination
Melanoma, basal cell carcinoma, and squamous cell carcinoma are the most common skin cancers. The vast majority are successfully treated with early diagnosis. It should not be forgotten that increased sun exposure in Turkey during the summer months is the cornerstone of cancer cases developing decades later.
Golden rule: at least once a year dermatological examination after the age of 30, showing suspicious "new" or "changing" moles to a doctor, knowing the ABCDE rule (Asymmetry, Border, Color, Diameter, Evolution). If there is a family history of skin cancer, patients with many moles, fair skin, and intense lifelong sun exposure may need more frequent follow-up.
Photoallergy and phototoxicity
Some medications (tetracycline, amiodarone, furosemide, some NSAIDs, some psychiatric medications) and cosmetic ingredients (bergamot oil, perfumes) can cause the skin to react in an unfamiliar way when combined with sun. These reactions sometimes resemble sunburn, sometimes present as eczema.
When you start a new medication, ask your doctor about sun interaction. Do not apply bergamot-containing perfume to the face; be careful with citrus oil contact.
Essence of the section:UV is a year-round burden. Although seasonal intensity increases, the habit of protection itself is not seasonal; it should become a lifelong habit both aesthetically and medically.