Ask a Maui Doctor: What Sunscreen Should I Use?

March 13, 2017, 11:15 AM HST · Updated March 13, 1:10 PM

Doctors at Minit Medical answer some of the questions submitted by readers.

Each week, a doctor from Minit Medical Kahului or Lahaina will answer questions that have been submitted by readers. Submit your own medical related questions to our doctors at [email protected]

Questions submitted will be considered for inclusion in the “Ask a Maui Doctor” column.

Q: I work outside all day long, what SPF sunscreen should I use to avoid getting burned?


A: Sunscreen application is one of the best ways to prevent against the aging and cancer causing effects of ultraviolet radiation. The multitude of sunscreen options available can make deciding which is the best and safest quite difficult. Deciding how well a certain sunscreen will protect you is based upon four main factors: SPF, UVA/UVB filtering ability, chemical vs. physical mechanism, and water resistance classification.

Ask a Maui Doctor: What sunscreen should I use to avoid getting burned? MauiNow Stock Photo.

Sun Protection Factor:

SPF, or “sun protection factor”, measures how well a sunscreen can block UVB radiation. The hot, red, painful burn that you experience after you spend too much time in the sun is mostly caused by UVB radiation. UVA radiation, also known as the “silent killer” due to its cancer causing effects, has a longer wavelength allowing it to penetrate and damage deeper layers.

So how much SPF do you need to prevent that burn? For those working or participating in outdoor activities, an SPF of at least 30 is recommended as it will block approximately 97% of UVB rays.

UVA/UVB Filtering Ability/Chemical vs. Physical Mechanism:

UVA/UVB filtering ability, also termed “broad spectrum”, is also an important aspect of sunscreen. Chemical sunscreens, such as Avobenzone, oxybenzone, etc. work by absorbing wavelengths of light so that your skin doesn’t.

Some chemicals absorb only one or the other so you need to have a sunscreen that provides coverage of both and says “Broad Spectrum” or UVA and UVB protective. Barrier sunscreens use a physical barrier, usually titanium dioxide or zinc oxide, and block both UVA and UVB radiation.

Water Resistance:

Lastly, we have water resistance classification of either no water resistance mentioned, water resistant, or very water resistant.

Water resistant sunscreen maintains its SPF rating after 40 minutes of use in water or during heavy perspiration, while very water resistant is good for 80 minutes of use.

How often you need to re-apply sunscreen depends on the activity and if you are in the water but usually you should re-apply every 90-120 minutes during direct sun exposure.

One last thing to consider is how sunscreens can kill our beautiful coral reefs. While no sunscreen is good for the coral reefs, look for one that is labeled “reef safe” if you will be in the water.

To sum it up, you should look for a sunscreen with a SPF of at least 30, broad spectrum UVA/UVB blocking ability, “reef” safe, and at least water resistant if you anticipate getting wet or sweating.



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