SPF Explained: How to Choose and Apply Sunscreen
SPF numbers are easy to misread. Here is what the FDA, the American Academy of Dermatology (AAD), the CDC and the Skin Cancer Foundation say, with a link to each source.
This guide is general information from public sources, not medical advice. Vanity Aisle is a retailer, not a medical provider. Every claim below links to the organization that made it, so you can read the original. Where sources disagree, we show both.
What SPF measures
The FDA says SPF mainly reflects protection against sunburn (UVB rays) and is not a time multiplier: SPF 15 does not mean you can stay in the sun 15 times longer. (FDA)
The CDC notes that the FDA discourages labels above SPF 50 because the extra protection is not clinically meaningful. (CDC Yellow Book: Sun Exposure in Travelers)
Broad spectrum
The FDA explains that broad spectrum means a sunscreen protects against both UVA and UVB rays. Products that are not broad spectrum, or that are below SPF 15, must carry a warning that they only help prevent sunburn, not skin cancer or early skin aging. (FDA)
Which SPF should you choose? The sources differ
| Organization | Recommendation | Source |
|---|---|---|
| FDA | Broad-spectrum, SPF 15 or higher | FDA |
| American Academy of Dermatology | Broad-spectrum, water-resistant, SPF 30 or higher | AAD: how to select sunscreen |
| Skin Cancer Foundation | SPF 30 or higher daily; SPF 50 or higher, water resistant, for long time outdoors | Skin Cancer Foundation |
| National Cancer Institute | At least SPF 15; notes some doctors suggest 30 or more | NCI |
How much to use, and when
| Question | What the sources say | Source |
|---|---|---|
| How much? | About 1 ounce (a shot glass) for the body; at least 1 teaspoon for the face (AAD). The CDC says about 2 tablespoons. The Skin Cancer Foundation says most people use less than half the right amount. | AAD: how to apply, CDC, Skin Cancer Foundation |
| How long before going outside? | About 15 minutes (AAD, FDA) or 30 minutes (Skin Cancer Foundation, NCI) | FDA, NCI |
| How often to reapply? | Every 2 hours, and right after swimming or sweating | FDA, AAD |
| Water resistant? | No sunscreen is waterproof. A water-resistant label must state 40 or 80 minutes. | FDA, Skin Cancer Foundation |
Mineral and chemical filters
The Skin Cancer Foundation describes mineral (inorganic) filters, such as zinc oxide and titanium dioxide, as sitting on the skin and mainly absorbing UV, and chemical (organic) filters, such as avobenzone, as absorbing UV and releasing it as heat. It says both kinds are tested as safe and effective, many products combine them, and mineral filters may irritate skin less. (Skin Cancer Foundation)
Sprays, spots people miss, and expiry
- Sprays: the FDA says never to spray directly on the face and to keep sprays away from flames, because some are flammable. The CDC suggests spraying onto your palms to apply to the face. (FDA, CDC)
- Spots people miss: ears, nose, back of the neck, hands, tops of the feet, hairline and scalp. Lips need their own SPF lip balm. (FDA)
- Expiry: the FDA says sunscreens must show an expiration date unless testing shows at least 3 years of stability. With no date, treat it as expired 3 years after purchase, and store it away from direct sun and heat. (FDA)
- Babies: the FDA does not recommend sunscreen for infants under 6 months; ask a doctor first.
- Insect repellent: the CDC notes DEET repellent may reduce a sunscreen’s SPF, by about 30 percent in some studies. (CDC)
Sunscreen is one part of sun protection
The AAD and FDA both advise seeking shade from about 10 a.m. to 2 p.m. and wearing long sleeves, a wide-brimmed hat and sunglasses. The NCI says UV rays are strongest between 10 a.m. and 4 p.m. and can pass through clouds and windows. (AAD, NCI)
Sources
- FDA: Sunscreen: How to Help Protect Your Skin from the Sun (fda.gov)
- AAD: How to select a sunscreen (aad.org)
- AAD: How to apply sunscreen (aad.org)
- AAD: Practice Safe Sun (aad.org)
- Skin Cancer Foundation: Sunscreen (skincancer.org)
- Skin Cancer Foundation: Tips on choosing and using sunscreen (skincancer.org)
- Skin Cancer Foundation: How to read a sunscreen label (skincancer.org)
- CDC Yellow Book: Sun Exposure in Travelers (cdc.gov)
- National Cancer Institute: Sunlight (cancer.gov)
