How to choose sunscreen from a dermatologistDermatologist Kwangho Yoo

Why should I wear sunscreen?

The reason why we should wear sunscreen when we go out in the morning or afternoon when the sun is not very strong is to protect against ultraviolet rays.

Ultraviolet A has a long wavelength, so it has the ability to penetrate deeply into the skin. In addition, the erythema index, which causes the skin to turn red, is 1,000 times lower than that of ultraviolet B, but it is the highest amount of ultraviolet rays that reach the earth's surface. Ultraviolet rays are commonly associated with pigmentation and photoaging, and UVA rays are the rays of UVA.

Ultraviolet B is a medium-wavelength ultraviolet ray, and unlike ultraviolet A, it is a high-energy ray, so it is known to cause skin cancer as well as short-term burns. Luckily, UVB rays can't penetrate glass windows, so it's safe indoors. Ultraviolet B rays are most polar at noon of the day, in proportion to sunlight, but UV-A rays are said to be irradiated consistently throughout the day, regardless of sunlight.

Mechanism of sunscreen

Sunscreens are divided into two main types according to their mechanism.

The first is a physical sunscreen that reflects light so that the skin can't absorb UV rays. Titanium and zinc, which are physical blockers, are known to be very effective in blocking both UVB and UVA rays. However, the disadvantage is that it seals the skin, which can cause acne, folliculitis, and cloudiness.

The second is a chemical sunscreen that allows the skin to absorb ultraviolet rays and then convert them into heat through chemical components. Chemical blockers do not produce a white castiness when applied to the skin, but they are more likely to cause allergies when used by people who are sensitive to chemical ingredients.

Criteria for choosing sunscreen

There are two levels to judge the efficacy of sunscreen: SPF and PA.

Among these, SPF stands for UVB, and PA stands for UVA. Many people think that the higher the SPF, the better the sunscreen. In fact, the difference between high and medium SPF is only about 2~3%, so it is okay to use SPF15 sunscreen in your daily life.

However, the US FDA recommends using a sunscreen with SPF 30. This is because if you don't apply enough of it, the expected effect will be lower than the actual SPF. In fact, studies have shown that for every 1/2 reduction in the amount of sunscreen applied, the protective effect of SPF is reduced by 1/4. It is recommended to apply a dose of 0.5 grams of sunscreen 30 minutes before sun exposure or every 2 hours.