Sunscreen guide: SPF vs PA, chemical vs mineral and how much to apply

TUREFF• •0

Sunscreen is the one skincare product almost every dermatologist agrees on. But the labels are confusing, and most people apply far less than the amount the protection on the label is based on. This guide explains what the numbers mean, how to choose, and how to use it properly. It is general information, not medical advice; if you have a skin condition or a concern about a mole, see a doctor or dermatologist.

UVA and UVB

Sunlight contains two kinds of ultraviolet light that matter for skin:

UVB mainly causes sunburn and plays a large part in skin cancer.
UVA penetrates deeper, contributes to skin ageing such as wrinkles and pigmentation, and also contributes to skin cancer. It passes through clouds and window glass.

A good sunscreen protects against both. Look for broad spectrum on the label.

SPF and PA

SPF (sun protection factor) measures protection against UVB. SPF 30 blocks more UVB than SPF 15, and SPF 50 slightly more again. No sunscreen blocks everything. Dermatology bodies generally recommend at least SPF 30 for daily use.
PA is a rating for UVA protection used in Korea, Japan and other Asian markets, shown with plus signs from PA+ to PA++++. More plus signs mean more UVA protection.
In Europe, a UVA logo in a circle means the UVA protection meets the EU's standard, and in the UK some products show a UVA star rating.

Chemical vs mineral

Chemical (organic) filters absorb UV light. They are usually lightweight and invisible on the skin, which is why so many Korean and Japanese sunscreens use them.
Mineral (inorganic) filters, zinc oxide and titanium dioxide, mostly reflect and scatter UV. They are often recommended for sensitive skin and children, but can leave a white cast, especially on darker skin. Newer formulas have improved this.
Many products combine both. The best sunscreen is one you like enough to use every day.

How much to apply

SPF is tested using 2 mg of sunscreen per square centimetre of skin, and most people apply much less, so they get much less protection than the label says.

For the whole body, the American Academy of Dermatology suggests about one ounce (roughly a shot glass) for an adult.
For the face, estimates vary between sources, from about a quarter of a teaspoon to half a teaspoon for the face and neck. Many people use the "two-finger rule": two finger-lengths of sunscreen for face and neck.
Do not forget ears, the back of the neck, the tops of the feet and your scalp if your hair is thin.

Reapplication

Sunscreen wears off. The AAD advises reapplying at least every two hours outdoors, and straight after swimming or sweating, even if the product says it is water-resistant. Indoor office days with little sun need less, but it is worth reapplying before heading out at lunchtime.

Under makeup

Apply sunscreen as the last step of your skincare and the first step before makeup. Let it set for a few minutes.
The SPF in foundation or tinted moisturiser is not enough on its own, because nobody applies foundation thickly enough.
To reapply over makeup, sunscreen sticks, cushions and sprays are convenient, though sprays are hard to apply evenly; use plenty and rub it in where you can.

Common myths

"I don't need sunscreen on cloudy days." Much UV gets through clouds.
"Darker skin doesn't need sunscreen." Darker skin burns less easily but can still be damaged, and sunscreen helps with pigmentation.
"SPF 100 means I can stay out all day." No sunscreen makes you sun-proof; reapply and seek shade.
"Makeup with SPF is enough." Only if you apply it very generously, which almost nobody does.
"Sunscreen stops you getting any vitamin D." Most people still make some, but ask a doctor if you are concerned about your levels.

The rest of sun protection

Sunscreen works best alongside shade, a wide-brimmed hat, sunglasses and covering up when the sun is strongest, usually around midday. Babies under six months should be kept out of direct sun rather than relying on sunscreen. What sunscreen do you use, or what question do you have about SPF and PA? Share your recommendations and questions in the comments.