Sunscreen Labels Decoded: SPF, PA++++, the UVA Circle and "Broad Spectrum"

Sunscreen labels pack a lot into a small space: a number, a few letters, sometimes a circle, a row of plus signs or a star rating. Each mark answers a different question, and the best-known one, SPF, answers only half of what you need to know. Here is how to read the whole label in under a minute.

SPF: protection against burning (UVB)

SPF, the sun protection factor, measures protection against UVB, the rays mainly responsible for sunburn. It is tested in a lab with a thick, even layer of product. The scale is not linear: SPF 15 is commonly said to block about 93% of UVB, SPF 30 about 97% and SPF 50 about 98%. Going from 30 to 50 is a smaller step than the numbers suggest, but a higher SPF gives you more margin when you apply too little, which most people do.

In the EU, SPF is grouped into categories: low (6 to 10), medium (15 to 25), high (30 to 50) and very high (50+). "50+" is the highest claim allowed there.

UVA: the half SPF doesn't measure

UVA rays penetrate deeper into the skin, contribute to skin ageing and, like UVB, to skin cancer risk. A high SPF alone says nothing about UVA. Different regions label it differently:

If you buy a sunscreen imported from another region, look for that region's UVA mark. A label with an SPF and no UVA claim at all is the one to question.

"Water resistant" is not "waterproof"

No sunscreen is waterproof. In the EU, "water resistant" means the product keeps at least half its protection after two 20-minute sessions in water, and "very water resistant" after four. In the US, labels state 40 or 80 minutes. Either way, reapply after swimming, heavy sweating or towelling off.

Reading the filters in the ingredient list

The UV filters are listed in the INCI list like any other ingredient. Mineral filters are zinc oxide and titanium dioxide. Organic (often called chemical) filters have longer names, for example butyl methoxydibenzoylmethane (avobenzone), octocrylene, or bis-ethylhexyloxyphenol methoxyphenyl triazine. Both types are tested for the protection on the label; the choice is mostly about texture, finish and how your skin tolerates them. Mineral filters can leave a white cast, especially on deeper skin tones.

The part the label can't promise: how much you use

Labs test sunscreen at 2 mg per square centimetre of skin. Studies have repeatedly found that people apply far less, often half or less, which means real protection can fall well below the number on the bottle. A common rule of thumb for the face and neck is two finger-lengths of product. Reapply about every two hours outdoors, and after swimming or sweating.

• SPF in makeup helps, but you would need a thick layer of foundation to reach the tested amount. Treat it as a bonus, not your sunscreen.
• Check the date. Sunscreen has an expiry date or an open-jar symbol (for example 12M). Heat degrades it, so don't leave it in a hot car.
• Sensitive skin or a medical condition? Ask a pharmacist or dermatologist which filters suit you.

What the label won't tell you, and reviews will

The label is a lab result. It can't tell you whether a sunscreen leaves a white cast on your skin tone, stings your eyes, pills under makeup or feels greasy by noon, which are exactly the reasons people stop wearing it. On Ratee, scan the bottle in the shop and read what people with your skin type say before you buy.