The Sunscreen Guide:
SPF, Mineral vs. Chemical, and How to Apply

Daily sunscreen is the single most effective habit for preventing skin cancer and premature aging. The rules are simple: choose a broad-spectrum sunscreen with SPF 30 or higher, apply enough (about one ounce for the body and a nickel-sized amount for the face), reapply every two hours outdoors and after swimming or sweating, and use it every day from spring through fall on Long Island, when the UV index is moderate to very high. Mineral and chemical sunscreens both work; the best sunscreen is the one you will actually wear. Sunscreen with SPF 15 or higher is also an eligible expense for a flexible spending or health savings account.

What Do SPF and Broad Spectrum Mean?

SPF (sun protection factor) measures protection against UVB, the rays that cause sunburn and most skin cancers. SPF 30 blocks about 97 percent of UVB, SPF 50 about 98 percent, and SPF 100 about 99 percent. The differences above 30 are small, but higher SPF gives a margin for the thin layer most people actually apply. Broad spectrum means the product also protects against UVA, the rays that penetrate deeper, drive wrinkles and sun spots, and contribute to melanoma. Choose both: broad spectrum and SPF 30 or higher, the standard recommended by the American Academy of Dermatology.

Mineral vs. Chemical Sunscreen: Which Is Better?

Both protect well when used correctly. The choice comes down to your skin and your preference.

Patients with rosacea, eczema, melasma, or easily irritated skin, young children, and anyone recovering from a laser treatment or surgery generally do best with a mineral sunscreen. For everyone else, the right sunscreen is the one you will apply generously every day.

How Much Sunscreen Should I Use?

• Body: about one ounce, the amount that fills a shot glass, for an adult in a swimsuit. Most people apply a quarter to half of that, which cuts the real SPF dramatically.
• Face and neck: a nickel-sized amount, or two finger-lengths squeezed along the index and middle fingers.
• Commonly missed spots: ears, the back of the neck, the part in your hair, the tops of the feet, the backs of the hands, and the lips (use an SPF 30 lip balm).
• Apply 15 minutes before going out so chemical sunscreens can bind to the skin. Mineral sunscreens work immediately.
• Reapply every two hours outdoors, and right after swimming, toweling off, or heavy sweating, even with water-resistant products.

What Does Water Resistant Mean?

No sunscreen is waterproof. “Water resistant” on a U.S. label means the SPF holds for 40 minutes of swimming or sweating; “very water resistant” means 80 minutes. After that time, or after drying off with a towel, reapply.

Which Sunscreen Is Right for My Situation?

• Babies under 6 months: shade, clothing, and hats rather than sunscreen. A small amount of mineral sunscreen on exposed areas is acceptable when shade is not possible.
• Children: a mineral sunscreen SPF 30 or higher, applied before school and camp and reapplied at midday. Stick formulas are easy for faces; sprays should be sprayed into the hands and then applied, never directly on the face.
• Sensitive skin, rosacea, or eczema: fragrance-free mineral sunscreen. See rosacea treatment.
• Melasma, dark spots, or deeper skin tones: a tinted mineral sunscreen containing iron oxides, which blocks visible light as well as UV and avoids the white cast of untinted zinc. See melasma treatment and dermatology for skin of color.
• Acne-prone skin: an oil-free, non-comedogenic sunscreen. Sunscreen does not cause acne when it is non-comedogenic, and some acne medications make skin more sun-sensitive, so it is essential.
• After a procedure or Mohs surgery: once the wound has healed, a mineral sunscreen on the scar for at least a year keeps it from darkening. See Mohs surgery aftercare.
• Sports and swimming: a very water resistant (80-minute) sunscreen, plus a rash guard or UPF shirt.
• Daily under makeup: a lightweight chemical or micronized mineral sunscreen as the last skincare step. SPF in foundation or moisturizer is a bonus, not a substitute, because the amount applied is too small.

Does Sunscreen Expire?

Yes. The FDA requires sunscreens to keep their strength for at least three years. Use the printed expiration date; if there is none, write the purchase date on the bottle and discard it after three years. Sunscreen that has separated, changed color, or been left in a hot car loses effectiveness sooner. A family that uses sunscreen correctly in summer will finish a bottle long before it expires.

Sunscreen Is One Layer, Not the Whole Plan

• Shade between 10 am and 4 pm, when UV is strongest. From May through August on Long Island the UV index is high to very high most afternoons.
• Clothing with a UPF 50 rating, a wide-brimmed hat (3 inches or more), and UV-blocking sunglasses.
• No tanning beds. Indoor tanning before age 35 raises melanoma risk by about 75 percent.
• Monthly self-checks and an annual skin exam. See how to check for skin cancer.

Frequently Asked Questions

Is SPF 50 better than SPF 30?

Slightly. SPF 30 blocks about 97 percent of UVB and SPF 50 about 98 percent, so the difference is small when sunscreen is applied correctly. In practice most people apply too thin a layer, and a higher SPF gives a margin of safety. The American Academy of Dermatology recommends broad-spectrum SPF 30 or higher; the amount you apply and how often you reapply matter more than the number.

Is mineral sunscreen better than chemical sunscreen?

Both protect well. Mineral sunscreens (zinc oxide, titanium dioxide) sit on the skin, work immediately, and are best for sensitive skin, rosacea, eczema, melasma, children, and healing skin. Chemical sunscreens absorb UV, feel lighter, and are easier to wear daily under makeup. The best sunscreen is the one you will apply generously every day.

How much sunscreen should I put on my face?

About a nickel-sized amount, or two finger-lengths squeezed along the index and middle fingers, for the face and neck. Apply it as the last skincare step before makeup and reapply every two hours when outdoors. The SPF in foundation or tinted moisturizer is a bonus, not a substitute, because the amount used is too small to deliver the labeled protection.

How often should I reapply sunscreen?

Every two hours while outdoors, and immediately after swimming, toweling off, or heavy sweating, even with water-resistant products. Water-resistant sunscreen holds its SPF for 40 minutes in water and very water resistant for 80 minutes. On an ordinary workday indoors, a morning application is usually enough unless you sit next to a sunny window.

Do I need sunscreen on cloudy days or in winter?

Yes for the face, year-round. Up to 80 percent of UV passes through clouds, and UVA, which drives aging and contributes to melanoma, is present all year and through window glass. In winter on Long Island the UV index is low, so sunscreen on the body is less critical, but snow reflects UV and skiing or winter sports still call for sunscreen on exposed skin.

Can babies and children use sunscreen?

Babies under 6 months should be kept in the shade and covered with clothing and a hat; a small amount of mineral sunscreen on exposed skin is acceptable when shade is not possible. From 6 months on, a mineral sunscreen SPF 30 or higher is recommended, reapplied every two hours outdoors. Sprays should be sprayed into the hands first, never directly onto a child’s face.

Does sunscreen cause acne or breakouts?

Not when it is oil-free and non-comedogenic. Heavy or greasy formulas can clog pores in acne-prone skin, so choose a lightweight gel, fluid, or mineral sunscreen labeled non-comedogenic. Sunscreen is especially important during acne treatment because retinoids, benzoyl peroxide, and some oral antibiotics increase sun sensitivity.

Is sunscreen FSA eligible?

Yes. Broad-spectrum sunscreen with SPF 15 or higher, including mineral sunscreens and SPF lip balm, is an eligible over-the-counter expense for flexible spending and health savings accounts, and since 2020 no prescription is required. Cosmetics that happen to contain SPF, such as foundation, are usually not eligible.

Related reading: how to check for skin cancer, skin cancer screening, melasma treatment, the month-by-month skin health calendar, and the patient education hub.