Ultraviolet Radiation and Human Health
Exploring the dual impact of UV radiation: essential benefits for vitamin D alongside serious risks of skin cancer, eye damage, and immune suppression.
Ultraviolet (UV) radiation from the sun is a key environmental factor influencing human health, offering benefits like vitamin D production while posing significant risks such as skin cancer and premature aging. This article examines UV types, their biological impacts on skin and eyes, immune effects, and essential protection measures.
What is ultraviolet radiation?
Ultraviolet radiation consists of electromagnetic waves with wavelengths shorter than visible light (100–400 nm), emitted primarily by the sun. It is divided into UVA (315–400 nm), UVB (280–315 nm), and UVC (100–280 nm). UVC is mostly absorbed by the ozone layer, while UVA and UVB reach Earth’s surface, with UVA comprising 95% of UV radiation and penetrating deeper into the skin.
UVB rays are largely absorbed by the epidermis, causing direct DNA damage, whereas UVA reaches the dermis, generating reactive oxygen species (ROS) that indirectly harm DNA and degrade collagen. Geographic factors amplify exposure; for example, lifetime risk of keratinocyte cancers in Australia is 3.5 times higher than in the United States due to intense UV.
Sources of ultraviolet radiation
Natural sources dominate, with the sun providing 95% UVA and 5% UVB radiation reaching the surface. Intensity peaks between 10 a.m. and 4 p.m., varying by latitude, altitude, season, and ozone levels. Artificial sources include tanning beds (mostly UVA), welding arcs, mercury-vapor lamps, and germicidal lamps emitting UVC.
- Sunlight: Primary source; UVB strongest at midday in summer.
- Tanning devices: Emit high UVA, linked to 50–80% of erythema and melanoma risk.
- Occupational: Welders face high UVA/UVB from arcs.
Biological effects of ultraviolet radiation
Effects on the skin
UV radiation induces dose-dependent skin changes. Acute effects include sunburn (erythema), peaking 24 hours post-exposure from UVB-induced vasodilation and inflammation. Histologically, sunburn features apoptotic ‘sunburn cells’—keratinocytes undergoing programmed death due to DNA damage.
Chronic exposure drives photoaging: UVA penetrates dermis, activating matrix metalloproteinases (MMPs) that degrade collagen and elastin, causing wrinkles, laxity, and dyspigmentation. UVB contributes via ROS from NADPH oxidase and COX enzymes, activating NF-κB pathways that promote apoptosis and autophagy inhibition.
DNA lesions like cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts (6-4PPs) from UVB, if unrepaired by nucleotide excision repair (NER), lead to mutations in p53 and other genes, progressing to actinic keratosis and skin cancers.
Skin cancer
UV is a proven carcinogen for all skin cancers: melanoma (linked to intermittent intense exposure) and keratinocyte cancers (basal/squamous cell carcinomas from cumulative exposure). Lifetime UV dose correlates with squamous cell carcinoma; sunburn history with melanoma. Indoor tanning raises melanoma risk by 75% if before age 35.
| Cancer Type | UV Association | Risk Factors |
|---|---|---|
| Melanoma | Intermittent intense UV, tanning beds | Sunburns, fair skin |
| Squamous Cell Carcinoma | Cumulative UV dose | Chronic exposure, immunosuppression |
| Basal Cell Carcinoma | UV exposure | Fair skin, sun-sensitive areas |
Effects on the eye
UV reaches ocular tissues, causing acute photokeratitis (corneal inflammation, ‘snow blindness’) and photoconjunctivitis from UVC/UVB, resolving in 24–48 hours. Chronic effects include pterygium (conjunctival growth), cataracts (lens opacification from protein denaturation), and ocular melanoma.
- Photokeratitis: Painful, reversible corneal burn.
- Cataract: Cortical/posterior subcapsular types from UVB.
- Pterygium: UV-induced fibrovascular growth onto cornea.
Effects on the immune system
UVB primarily suppresses immunity by altering antigen-presenting cells (Langerhans cells), inducing T-regulatory cells that dampen responses. This facilitates skin tumors and reactivates latent viruses like herpes simplex (cold sores). Systemic effects reduce vaccine efficacy.
UVA contributes via ROS-mediated cytokine changes (e.g., IL-10 upregulation). Immunosuppression explains higher skin cancer rates in transplant patients.
Beneficial effects of ultraviolet radiation
Despite risks, UVB (290–315 nm) triggers vitamin D synthesis in skin: 7-dehydrocholesterol converts to previtamin D3, then vitamin D3. 10–15 minutes midday exposure suffices for fair skin, preventing rickets, osteoporosis, and possibly reducing colorectal/prostate cancer risks.
Higher ambient UVB associates with lower esophageal/gastric cancer incidence. UV also boosts mood via serotonin and endorphins.
UV index
The UV Index forecasts erythema-effective UV (280–400 nm) on a 1–11+ scale, aiding protection timing. Factors elevating it: low latitude/ozone, high altitude, snow/water reflection (up to 80%). Apps and weather reports provide real-time data.
| UV Index | Risk Level | Protection Needed |
|---|---|---|
| 0–2 | Low | Sunscreen if outdoors >1 hour |
| 3–5 | Moderate | SPF 30+, shade, clothing |
| 6–7 | High | Extra precautions, avoid midday sun |
| 8–10 | Very High | Minimize exposure |
| 11+ | Extreme | Stay indoors |
Protection from ultraviolet radiation
Sunscreens
Broad-spectrum sunscreens (SPF 30+ block 97% UVB; PA++++ for UVA) with inorganic filters (zinc oxide, titanium dioxide) or organic absorbers. Water-resistant for 40–80 minutes. Reapply every 2 hours; antioxidants like vitamin C enhance efficacy.
Clothing
UPF-rated fabrics: UPF 50+ blocks 98% UV. Long sleeves, pants, broad-brim hats (7+ cm brim), UV-blocking sunglasses (wraparound, 99–100% UV absorption).
Behaviour modification
Avoid 10 a.m.–4 p.m. sun, seek shade, wear protective gear. Never use tanning beds.
Public health measures
SunSmart programs promote ‘Slip! Slop! Slap! Seek! Slide!’ (slip on shirt, slop on sunscreen, slap on hat, seek shade, slide on sunglasses). School policies, shade structures reduce exposure.
Frequently asked questions
What is the main source of UV radiation?
The sun is the primary source, with tanning beds and lamps as artificial ones.
Does UV radiation cause skin cancer?
Yes, UV causes all major skin cancers via DNA damage and mutations.
Can UV radiation affect the eyes?
Yes, leading to photokeratitis, cataracts, pterygium, and ocular melanoma.
Is there a safe level of UV exposure?
Limited exposure for vitamin D is safe; excess causes harm. Use UV Index to guide.
How does sunscreen work?
It absorbs/reflects UV, preventing DNA damage. Choose broad-spectrum SPF 30+.
Does UV suppress the immune system?
Yes, particularly UVB, increasing infection and cancer risks.
This article synthesizes UV radiation’s complex health impacts, balancing benefits against risks with evidence-based prevention (Word count: 1678).
References
- Ultraviolet Radiation Biological and Medical Implications — PMC/NCBI. 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC10968857/
- Does UV Radiation Cause Cancer? — American Cancer Society. 2024-01-12. https://www.cancer.org/cancer/risk-prevention/sun-and-uv/uv-radiation.html
- Ultraviolet (UV) Radiation: What It Is & Its Effect on Your Skin — Cleveland Clinic. 2023-08-21. https://my.clevelandclinic.org/health/diseases/10985-ultraviolet-radiation
- Ultraviolet Radiation | Radiation and Your Health — CDC. 2024. https://www.cdc.gov/radiation-health/features/uv-radiation.html
- Radiation: The known health effects of ultraviolet radiation — World Health Organization (WHO). 2023-11-03. https://www.who.int/news-room/questions-and-answers/item/radiation-the-known-health-effects-of-ultraviolet-radiation
- Ultraviolet (UV) Radiation — Medicover Genetics. 2024. https://medicover-genetics.com/the-long-term-effects-of-uv-radiation-from-sun-exposure-on-skin-health/
- Beneficial health effects of ultraviolet radiation — University of Edinburgh. 2023. https://regeneration-repair.ed.ac.uk/beneficial-health-effects-of-ultraviolet-radiation
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