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How Much SPF Do You Need In Your Sunscreen?

Summer is here, and that means spending time in the sun. Ade Adamson, assistant professor of dermatology at Dell Medical School, explains what you need to know about sun protection.

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Sun Screen

Summer is here, and that means spending time in the sun. Skin protection is a hot topic this time of year, but do you know how much SPF you really need when you head outside?

SPF stands for Sun Protection Factor, and it represents the ability of sunscreen to protect against ultraviolet B (UVB) radiation that burns skin and can lead to skin cancer and signs of aging.

In the past, SPF 30 was the highest you could get. Now, companies are offering higher and higher SPF options in the triple digits, each promising more sun protection than the next.

Even the most seasoned sunbathers can be overwhelmed by the variety of options these days.

We spoke with Ade Adamson, an incoming assistant professor of dermatology at Dell Medical School beginning July 1, to set the record straight on sunscreen.

Q: There’s been debate about whether using SPF over 50 really makes a difference. Some people say anything higher is just marketing. Is that true? How much SPF do people need?

Ade Adamson: The amount of UVB radiation blocked by SPF 15, 30, 50, 100 sunscreen is 93 percent, 97 percent, 98 percent and 99 percent, respectively. So, doubling the SPF does not double the amount of protection one gets from sunscreen. If you apply sunscreen appropriately, the benefit from higher SPF amounts is marginal. However, most people do not apply a thick enough layer, so their SPF 30 may be more like an SPF 20. I usually recommend patients use an SPF 50+ so that they are covered if they do not apply their sunscreen very well.

“I usually recommend patients use an SPF 50+ so that they are covered if they do not apply their sunscreen very well.” – Ade Adamson

Q: Could there be any harm in getting a really high SPF sunscreen?

AA: There is no evidence to suggest really high SPF is harmful for human health.

Sometimes people say that you’re less likely to get burned if you have a base tan. Is this true?

AA: The base tan is a commonly held misconception. When you get a tan, that’s the body’s response to injury from UV rays. Therefore, getting a base tan is actually promoting injury to the skin. The effectiveness of a base tan has been studied before, and it only offers SPF of 3 or less. That is an incredibly low level of protection. Therefore, dermatologists recommend using sunscreen as sun protection and not base tanning.

“The effectiveness of a base tan has been studied before, and it only offers SPF of 3 or less.” – Ade Adamson

Q: Does how much SPF you need vary by skin type? Do people with darker skin need sunscreen?

The lighter your skin, the more easily it will get burned by the sun’s UV rays. However, all skin types can get sun burned and suffer damage from UV rays. Therefore, dermatologists recommend that everyone use sunscreen of at least SPF 30.

Q: How frequently should people reapply? How much sunscreen do people need to lather on to get the advertised sun protection?

AA: Sunscreen should be used daily, but most importantly it should be used when you know you are going to be outside in sunlight for a long time. Remember to reapply sunscreen every 2-3 hours because its protection wears off over time. You should apply 1 shot glass full (about 1 to 1.5 ounces) of sunscreen to cover your entire body. This works out to about a teaspoon for your face and 1 teaspoon for each arm/hand.

Q: What about when you are swimming?

AA: It is important to understand that no sunscreen is waterproof. In 2011, the Food and Drug Administration banned the use of “waterproof” on marketed sunscreens. However, sunscreen manufacturers can market “water resistant” and “very water resistant” for their products. “Water resistant” means that the sunscreen maintains its level of SPF protection after 40 minutes, while “very water resistant” maintains protection after 80 minutes.

Q: You can get sunscreen in different forms these days – cream, lotion, spray, for example. Are these equally effective?

AA: Creams, lotions and sprays are equally as effective in theory. However, in practice it’s a different story. In the real world, people tend to apply spray sunscreen as if its “spray and walk away” cologne. As a result, people get less protection. As a rule, you should spray five seconds’ worth of sunscreen on each general body part, then rub it in so that you get adequate protection.

Q: What are the most important things people should look for when reading a sunscreen label?

AA: SPF only measures UVB and not UVA, which can also damage the skin. For this reason, dermatologists recommend looking for sunscreens that specify that they are “broad spectrum,” meaning they cover both UVA and UVB rays.

Q: Is it true that you can get a sun burn or sun damage even on a cloudy day?

AA: As much as 80 percent of UV rays pass through the clouds and reach earth. The higher your altitude, the stronger the UV rays. This means people living in Denver get stronger UV rays than people in Kansas. Most normal glass windows block UVB rays, but they do not block UVA, which can cause sun damage and skin cancer. You may have an awesome corner office with floor-to-ceiling windows, but it comes with an extra dose of UV radiation, so sun protect accordingly!

Q: Can sunscreen go bad? Like if you leave it in the heat? 

AA: It is not good for sunscreen to sit out in the sun or be left inside of a hot automobile, because the ingredients are not stable in the heat. If you are at the beach/pool, try to place your sunscreen in a shaded area or at least underneath a towel away from direct sunlight. Another creative alternative is placing your sunscreen in your cooler at the beach so that when you reapply, your skin can get a nice cool-down as well.

Q: So, we’ve talked about what kind of sunscreen people should use and how much they should use. What about where people should apply it? Are there any spots that are commonly overlooked?

AA: Remember to put sunscreen on your ears! Skin cancer on the ears can be more difficult to treat and require surgery that, depending on the location, can leave the ears looking like they have been nibbled on. The lips are also susceptible to UV damage, so always look for lip balm containing SPF 30.

Ade Adamson


Dr. Adamson will begin July 1 as an assistant professor in the Department of Internal Medicine at Dell Medical School at UT Austin, where he will engage in teaching, research and clinical care. He is a general dermatologist who sees patients with conditions ranging from acne to psoriasis to skin cancer. His primary clinical interest is caring for patients at high risk for melanoma of the skin, such as those with many moles (particularly atypical moles) or a personal and/or family history of melanoma. His academic research focus involves improving the quality of care delivered to patients with skin disease, particularly those with skin cancer.