UVA vs UVB rays: complete guide to understanding UV radiation and sun protection

UVA rays penetrate deep into skin causing premature ageing, whilst UVB rays are responsible for sunburns. Both increase skin cancer risk and require proper sun protection with broad-spectrum sunscreen.

What are ultraviolet (UV) rays and why are they important?

Ultraviolet (UV) radiation is one of the main threats to skin health. Since the skin is the body's largest organ, understanding the difference between UVA and UVB rays is crucial to maintaining a healthy skin balance and preventing long-term damage.

There are three types of UV radiation: UVA, UVB, and UVC. UVC rays are blocked by the ozone layer and do not reach the Earth's surface, meaning the main concern is protection from UVA and UVB rays.

UVA rays: the "Ageing Rays"

UVA Ray Characteristics (320-400 nm):

• Longer wavelength than UVB
• Penetrate deep into epidermis and dermis
• Present throughout the day, even morning and late afternoon
• Pass through window glass

How UVA rays affect your skin

UVA rays are further subdivided into:

• UVA I (340-400nm) - also called "far UVA"
• UVA II (320-340nm) - known as "near UVA"

The primary characteristic of UVA rays is their ability to penetrate deep into the skin. Scientific research has demonstrated that multiple low-dose exposures to UVA radiation in humans are associated with significant histological changes in both the dermis and epidermis.

Important: Even highly photosensitive patients may experience difficulties indoors, as UVA rays can penetrate window glass.

UVB rays: the "Burning rays"

UVB Ray Characteristics (290-320 nm):

• Shorter wavelength compared to UVA
• Primarily responsible for sunburn
• Blocked by most car glass and windows
• Most intense during midday hours

The positive role of UVB rays in Vitamin D synthesis

Not all effects of UVB rays are negative. In fact, UVB radiation is essential for vitamin D synthesis. In the epidermis, 7-dehydrocholesterol is converted into vitamin D (cholecalciferol) precisely due to UVB exposure.

Vitamin D is crucial for:

• Calcium absorption from the intestinal tract
• Maintaining strong bones
• Preventing rickets in children
• Preventing osteomalacia in adults

Harmful effects of UV radiation on skin

Immediate and long-term skin damage

Immunosuppression

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Reduced immune response

Tumori cutanei

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Premalignant & malignant lesions

Premature aging

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Wrinkles, elasticity loss

Chronic sun exposure causes several scientifically documented negative effects:

Skin Cancer and UV radiation

Basal Cell Carcinoma (BCC): the most common skin cancer, primarily affecting face and head. In Caucasians, the lifetime risk of developing BCC is 30%.

Squamous Cell Carcinoma (SCC): The most important risk factor is cumulative sun damage. In a case-controlled study, risk was greatest in those with more than 30,000 hours of cumulative lifetime sun exposure.

Melanoma: the most serious form of skin cancer. Intense and intermittent sun exposure at a young age significantly increases melanoma risk. Individuals with five or more severe sunburns during childhood or adolescence have an estimated twofold greater risk of developing melanoma.

Critical Fact: using tanning beds before age 35 increases cutaneous melanoma risk by 75%.

Choosing the right sun protection

SPF and broad-spectrum protection

The Sun Protection Factor (SPF) primarily measures the absorption of UVB rays :

SPF 15

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93,3% UVB protection

SPF 30

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96,7% UVB protection

SPF 50

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98% UVB protection

Types of sunscreen filters

Chemical sunscreens: organic aromatic compounds that absorb high-intensity UV radiation and convert it to longer, lower-energy wavelengths.

Physical sunscreens: inorganic compounds like titanium dioxide and zinc oxide that reflect, scatter, and/or absorb UV radiation.

Sun protection best practices

Golden rules for sunscreen application

• Apply 15-30 minutes before sun exposure
• Reapply every 2 hours or more frequently when swimming
• Use broad-spectrum products with SPF of at least 15
• Don't forget lips, ears, neck, décolleté and scalp

When sun protection is most critical

Sunscreens are particularly important:

• April to october
• Between 10 AM and 2 PM (peak UV intensity hours)
• Even on cloudy days (up to 80% of UV rays penetrate clouds)
• Whilst driving (UVA rays pass through car windows)

Sunscreen side effects and solutions

In a longitudinal study of 603 subjects applying daily sunscreen, 19% developed adverse reactions, with the majority being irritant in nature. Common problems include:

• Stinging or burning around the eye area
• Contact dermatitis caused by PABA, PABA esters, benzophenones
• Acne breakouts primarily due to the vehicle rather than active ingredients

Solution: Choose gels or sprays with less oil content if you have oily or acne-prone skin.

Banned sunscreen filters in Europe: what to avoid?

Certain chemical sunscreen filters have been banned or restricted in Europe due to potential health risks and environmental concerns. Here are the main ones:

1. Oxybenzone (Benzophenone-3)
2. • Disrupts the endocrine system, affecting hormone balance.
   • Damages coral reefs, contributing to marine ecosystem degradation.
3. Octinoxate (Ethylhexyl Methoxycinnamate)
4. • Linked to hormonal disruption, affecting the endocrine system.
   • - Banned in some European countries due to its environmental impact.
5. Homosalate
6. • Under review for potential negative effects on hormone regulation.
   • Can accumulate in the body, leading to hormonal imbalances.
7. Octocrylene
8. • Breaks down into benzophenone, a controversial substance.
   • May cause skin irritation and allergic reactions.
9. Avobenzone
10. • Unstable in sunlight, generating free radicals.
    • Can react with chlorine, leading to skin irritation.

New FDA sunscreen regulations

In June 2011, the US FDA introduced new sunscreen labelling guidelines:

• Broad-spectrum definition: UVA protection that increases proportionally with UVB protection
• Mandatory warnings for products with SPF below 15
• Prohibition of terms like "waterproof" and "all day protection"
• Water resistance duration specification (40 or 80 minutes)

Sunscreen vehicle types

• Lotions (Oil-in-water/Water-in-oil)
• • The most common formula is easy to apply, but it can feel greasy on the skin
  • The "sport" or "ultra-sheer" versions offer a lighter texture and are less greasy on the skin.
• Gel
• • Water-based formula, absorbs quickly, perfect for oily skin.
  • Less greasy, but can be easily removed by sweat, requiring frequent reapplications.
• Sprays
• • Ideal for protecting the scalp, easy to apply on hard-to-reach areas.
  • Hard to apply evenly, so it's best to layer and blend well for complete protection
• Sticks
• • Lipid-based formulas, perfect for lips, nose, and eye contour areas.
  • Compact, waste-free, and convenient for on-the-go application.
• Cosmetics
• • Foundation with SPF 4-30 provides daily sun protection with matte coverage, but it may not be enough for prolonged sun exposure.
  • Tip: Apply first SPF 50 sunscreen for optimal protection before applying makeup.

Conclusion: sun protection as a health investment

Understanding the difference between UVA and UVB rays is the first step towards effective sun protection. Whilst UVB rays cause immediate sunburn, UVA rays cause cumulative damage that manifests over time as premature ageing and increased skin cancer risk.

Regular use of broad-spectrum sunscreens with SPF of at least 15, combined with protective clothing and avoiding peak sun hours, currently represents the best preventive measure for maintaining skin health.

Remember: investing in sun protection today means preserving your skin's health and beauty for the future.

Leterature

1. Dale Wilson B, Moon S, Armstrong F. Comprehensive review of ultraviolet radiation and the current status on sunscreens. J Clin Aesthet Dermatol. 2012 Sep;5(9):18-23. PMID: 23050030; PMCID: PMC3460660.
2. Brar G, Dhaliwal A, Brar AS, Sreedevi M, Ahmadi Y, Irfan M, Golbari R, Zumárraga D, Yateem D, Lysak Y, Abarca-Pineda YA. A Comprehensive Review of the Role of UV Radiation in Photoaging Processes Between Different Types of Skin. Cureus. 2025 Mar 24;17(3):e81109. doi: 10.7759/cureus.81109. PMID: 40276407; PMCID: PMC12018068.