Answers to Your Top SPF Questions

With sunny summer days ahead, sunscreen should be on the top of your mind. Our dermatologists are always getting questions from patients about SPF usage. Use their answers to help prepare you for a summer full of safe fun in the sun.

Is a high-number SPF better than a low-number one?

We recommend using a sunscreen with an SPF of 30 or above, which blocks 97 percent of the sun’s UVB rays. While higher-number SPFs block slightly more of the sun’s UVB rays, there are no sunscreens that can block 100 percent of the sun’s UVB rays. It is very important to remember that SPFs with higher numbers do not last longer than low-number SPFs. In other words, an SPF with a higher number does not mean you can spend additional time outside without reapplying it. Any sunscreen, regardless of number, should be reapplied about every two hours when spending time outside, even on cloudier days. You should also reapply after swimming or sweating.

Why do I need a broad-spectrum SPF?

The two basic types of ultraviolet rays that reach the earth’s surface are UVB and UVA rays. The UVB can produce sunburn and also plays the biggest role in causing skin cancers, including melanoma. UVA rays can also contribute to skin cancer formation. The UVA rays, which penetrate more deeply into the skin, are responsible for premature aging of the skin. You want a sunscreen that says “broad-spectrum” to protect your skin from both UVB and UVA damage.

How much sunscreen should I apply?

Most adults need about 1 ounce — or enough to fill a shot glass — to fully cover their body and about 1/2 a teaspoon to cover the face.

If my makeup has SPF in it, do I still need to apply sunscreen to my face?

Some people apply their makeup with sunscreen and believe this is sufficient to protect them, but in reality, unless the makeup is being applying in a thick layer, it doesn’t block ultraviolet radiation effectively enough. You still need to apply an SPF under your makeup. Or you can use a mineral powder formulated sunscreen on top of your makeup. – Dr. Rachel Nazarian

What is the difference between mineral and chemical sunscreens?

“They are both proven to be safe and effective in reducing short and long term sun damage, and reducing the risk of sun damage and skin cancer,” says Dr. Deborah Spey. “The difference is how they accomplish that. Chemical sunscreens contain chemicals which act like a sponge, absorbing the ultraviolet rays. Mineral sunscreens contain zinc oxide or titanium dioxide and reflect the rays, shading and physically shielding the skin from harmful UV.”

Should I be worried about the ingredients in my sunscreen?

According to Dr. Rachel Nazarian: “There is a lot of fear mongering about ingredients in sunscreen. The reality is that many people die from preventable skin cancers every day, which could be avoided with diligent and appropriate application of sunscreen. The evidence supporting safety in sunscreen is increasingly reassuring. With any product, some ingredients may be less tolerable in people who have sensitive skin, but these ingredients are beautifully tolerated by most people and allow the product to be cosmetically elegant and applied smoothly, which increases compliance of the product and makes people want to apply to daily.”