UVA vs UVB Filters — What's the Difference and Why You Need Both
UVA accelerates ageing and causes melanoma; UVB triggers sunburn. Learn what Broad Spectrum, PA++++ and PPD mean and how to read sunscreen labels.
Two types of radiation — two different threats
The sunlight that reaches the Earth's surface contains two types of ultraviolet radiation that matter dermatologically: UVA (315–400 nm) and UVB (280–315 nm). Although both damage the DNA of skin cells, their mechanism of action and their health consequences are fundamentally different. Understanding this distinction is the key to choosing sun protection wisely.
UVC radiation (100–280 nm) is almost entirely absorbed by the ozone layer and never reaches the skin under natural conditions — which is why, when it comes to photoprotection, we focus solely on UVA and UVB.
UVA — the silent driver of ageing and melanoma
UVA accounts for roughly 95% of the UV radiation that reaches the Earth. Its intensity stays relatively constant all year round — it passes through clouds, car windows and thin fabrics. Unlike UVB, UVA rays penetrate deeply, reaching all the way down to the dermis, where they break down collagen and elastin fibres.
The consequences of chronic UVA exposure include:
- Photoageing — wrinkles, loss of firmness and pigmentation spots. It's estimated that up to 80% of the visible signs of skin ageing are caused by UV exposure, mainly UVA.
- Malignant melanoma — epidemiological studies have shown a strong link between UVA exposure and the development of melanoma, the most dangerous form of skin cancer.
- Immunosuppression — UVA weakens the skin's local immune response, reducing the body's ability to eliminate damaged cells.
Crucially, UVA causes neither redness nor stinging — the skin sends no warning signal. The damage builds up over the years with no visible symptoms, which is exactly what makes UVA so dangerous.
UVB — sunburn and squamous cell carcinoma
UVB makes up just 5% of the UV radiation reaching the Earth's surface, but its energy is far higher than that of UVA. UVB rays act mainly on the epidermis and are directly responsible for:
- Sunburn (erythema) — redness, pain and, in severe cases, blisters. The minimal erythemal dose (MED) depends on your skin's phototype.
- Squamous cell carcinoma (SCC) — the second most common skin cancer, strongly linked to cumulative UVB exposure.
- Actinic keratoses — precancerous lesions that can progress into SCC.
UVB intensity changes throughout the day (peaking between 10 a.m. and 4 p.m.) and across the year (highest in summer). UVB does not pass through glass — which is why you won't get sunburnt behind a car window, even though UVA-driven ageing continues.
Broad Spectrum — what does it really mean?
The SPF (Sun Protection Factor) measures protection against UVB only. A sunscreen with SPF 30 tells you nothing about UVA protection. That's why the Broad Spectrum label matters — it guarantees protection against both types of radiation.
In Europe, the Colipa standard applies (now Cosmetics Europe): a sunscreen may carry the UVA-in-a-circle mark only if its UVA protection is at least one third of the SPF value. This means an SPF 30 product must provide UVA protection of at least PPD 10.
PA++++ and PPD — how is UVA protection measured?
UVA protection is expressed through several systems:
- PPD (Persistent Pigment Darkening) — an in vivo method that measures skin darkening after UVA exposure. PPD 10 means a tenfold increase in the time it takes for darkening to appear.
- PA+ to PA++++ — a Japanese classification system based on PPD. PA++++ corresponds to PPD ≥ 16, the highest level of UVA protection.
- Boots Star Rating — a system used in the United Kingdom that rates the ratio of UVA to UVB protection on a scale from 1 to 5 stars. Five stars means UVA protection is almost equal to UVB.
When choosing a sunscreen, look for products with PA++++ or the European UVA mark. These labels guarantee that protection against ageing rays is at an adequate level. Check your sunscreen's formula in our ingredient database to identify the specific UVA filters it contains.
How to choose the right protection
When picking a sunscreen, follow these principles:
- SPF 30 minimum — blocks 97% of UVB. SPF 50 blocks 98%, so the difference is minimal.
- The Broad Spectrum label or the European UVA mark — your guarantee of protection against both types of radiation.
- PA+++ or PA++++ — if the product comes from the Asian market, choose the highest category.
- Reapply every 2 hours — no filter lasts indefinitely. Reapply after swimming, sweating or towelling off.
You can read more about choosing the right SPF level in our guide SPF in sunscreens — how much do you really need?
Summary — UVA protection is just as important as UVB
For years the cosmetics industry focused on SPF while ignoring UVA protection. Today we know that UVA is responsible for skin ageing and melanoma, while UVB causes sunburn and squamous cell carcinoma. Complete photoprotection requires defence against both types of radiation — so always choose products with confirmed broad-spectrum protection.
Want to find out whether your sunscreen protects against UVA? Search for it in our database and review its list of active ingredients.
FAQ
No — SPF measures protection against UVB only. UVA protection is confirmed by labels such as PA++++, PPD or the European UVA-in-a-circle mark (Colipa). Always look for the Broad Spectrum label.
UVA is the main cause of photoageing, because it penetrates deep into the dermis and breaks down collagen and elastin. It's active all year round, even through windows and clouds.
PA++++ is the highest UVA protection category in the Japanese system, corresponding to a PPD value of ≥ 16. It means at least a sixteenfold increase in the time it takes for UVA-induced darkening to appear.
No — standard window glass blocks most UVB, which is why you won't get sunburnt behind glass. UVA, however, does pass through glass, meaning photoageing continues even inside a car.
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