Are You Using Enough Sunscreen?What Studies Show
SkinArticleThe SPF on the bottle is measured with a thick layer of 2 milligrams per square centimeter. In everyday life, studies find people apply about a quarter to a half of that, and protection drops fast: in a Danish test, using half the amount gave roughly the square root of the SPF. People also miss parts of the face, especially the eyelids. Here is how much to use and simple ways to close the shortfall.
In this article
You chose a high SPF and put it on every morning. But the number on the bottle assumes a much thicker layer than most people use.
The amount behind the number
SPF is tested with 2 milligrams of sunscreen per square centimeter of skin.1 A review from Copenhagen found that, in everyday use, people apply about 0.39 to 1.0 milligrams, a fraction of that, which cuts protection considerably.1
How fast protection drops
In a Danish test on 20 volunteers, researchers applied the same sunscreen at four different thicknesses and measured the protection it gave.2
- Protection rose and fell steeply with the amount.2
- Using half the test amount gave roughly the square root of the SPF.2 The study used an SPF 4 product, but if the same pattern held, an SPF 30 used at half thickness would act more like SPF 5 or 6.
- Using a quarter gave roughly the fourth root.2
The spots people miss
Researchers in Liverpool photographed 84 people, most of them women, with a UV camera after they put on SPF 30.3
| Sunscreen | SPF moisturizer | |
|---|---|---|
| Share of face missed | 11.1%3 | 16.6%3 |
| Share of eyelid area missed | 14.0%3 | 20.9%3 |
People didn’t realize they’d missed these areas.3
How to close the shortfall
- Use more. Most adults need about 1 ounce, roughly a shot glass, to cover skin that clothing doesn’t.4
- Put it on before going out, then reapply once within the first hour; the Copenhagen researchers suggest this simple two-step habit to make up for thin first coats.1
- Reapply every 2 hours outdoors, and after swimming or sweating.4
- Don’t forget the neck, ears, tops of the feet, and the eyelid area.43
- A very high SPF, 70 to 100, can partly make up for using too little.1
See how to choose and use sunscreen and does sunscreen cause vitamin D deficiency?
Try: “I wear SPF 50 every day but still burn on my nose and around my eyes. Am I using enough, and is there a product that’s easier to apply near my eyes?”
Skin, Head to Toe covers daily sunscreen in Chapter 5, “Oily by Noon, Tight by Bedtime,” in a section called “Your Shelf,” where sunscreen is one of four things every Shelf holds. See the book.
This article is for general educational purposes only and is not medical advice. It isn't a substitute for diagnosis or treatment from a qualified healthcare professional who knows your health history. Sunscreen is one part of sun protection, alongside shade, clothing and hats. See a dermatologist for a new or changing mole or a sore that doesn't heal. Girl Playbook does not endorse any specific product, test, or provider.
Girl Playbook sells this book. It provides education and worksheets, not individualized medical care.
Sources
The research behind this article, in the order it’s cited. How we source our articles.
- Photodermatology Photoimmunology and Photomedicine (abstract via PubMed), 2014Application of sunscreen--theory and reality (opens in a new tab)abcd
- British Journal of Dermatology (abstract via PubMed), 2007The relation between sun protection factor and amount of suncreen applied in vivo (opens in a new tab)abcd
- PLOS ONE journal (via PubMed Central), 2019Application of SPF moisturisers is inferior to sunscreens in coverage of facial and eyelid regions (opens in a new tab)abcdefg
- American Academy of Dermatology, 2026How to apply sunscreen (opens in a new tab)abc
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