[Dr. Jeon's Secret to Healthy Skin] Unnoticeable Common Sense about Sunscreens ②
[Dr. Jeon's Secret to Healthy Skin] Unnoticeable Common Sense about Sunscreens ②
  • 전혜찬 더서울피부과 원장ㅣ번역·김성혜 인턴기자 (desk@k-health.com)
  • 승인 2020.07.17 14:40
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Dr. Hye Chan Jeon, the director of The Seoul Dermatology

In continuation of the previous column, I will explain more about sunscreens. Last time I advised on applying sunscreen every two hours if using less than required. But you may worry that doing so will cause skin irritations. Will it?

Actually, quite a lot of my patients complain of dermatitis and folliculitis caused by either irritation from trying to wash off sunscreen or pore blockages and oil due to sunscreen. To understand why this phenomenon occurs, you first need to know about the ingredients of sunscreens.

■ Physical vs. Chemical Sunscreens

You may have often heard about physical and chemical sunscreens.

First, physical sunscreens reflect the sunlight with zinc oxide and titanium dioxide. There’s a high possibility that white cast will occur, but when produced as nanoparticles to decrease white cast, problems with active oxygen and lung damage arise, and so white cast is inevitable.

On the other hand, people misunderstand chemical sunscreens as harmful. This is not only because it may cause photoallergic reactions, but also, its ingredients like oxybenzone and octinoxate caused deaths of coral reefs in Hawaii, resulting in a prohibition on the sale, distribution, and use of chemical sunscreens since 2021.

Sunscreens are the biggest reason for photoallergic reactions. However, it has a low incidence rate of less than 1%. Although sunscreens seem to be the cause, many of the patients visit our clinic with sunburns or phototoxicity.

This means reactions occurring right after exposure to sunlight are often phototoxic reactions, not photoallergic, because cosmetics, hair dye, cigarettes, and pesticides contain various drugs and their derivatives.

Physical sunscreens are known to cause pore blockage instead of photoallergic reactions. Is this true?

This has to do with water resistance rather than physical sunscreen. If SPF is maintained just like when first applied after 20 minutes and going into the water twice, then it is marked as "water-resistant." If still retained after going into the water for 4 times, then it is labeled as "very water-resistant."

Just as you use silicon to mend water leaks, cosmetics also contain a lot of silicon ingredients. Silicon ingredients are the cause of the perception that sunscreens smell bad. Just like silicon primer block pores, causing hair folliculitis so is water-resistant sunscreen. If sunscreens block pores, then inflammations of sebaceous glands like comedonal acne and folliculitis can commonly occur.

We think waterproof products are good, but it’s not always so. Water-resistant sunscreens should be used depending on the purpose like outdoor activities, water leisure, or commute. When applied water-resistant sunscreen, you need to double cleanse since it doesn’t wash off with just water or face wash, causing damage to the skin barrier. To prevent acne and skin inflammation, use water-resistant sunscreens only when necessary and wash it off in a way that least irritate the skin.

■ The Relation between UV rays and Clothes

Nowadays, not only sunscreens but also clothing is grabbing attention. I should begin by saying that the color of clothes and UV rays are irrelevant.

The UV protection factor (UPF) tells the sunshade effects of clothes. According to research, when three different dyes of the same concentration and color were used on a cotton material, UPF changed depending on the dye, which implies that reflected color or visible rays are unrelated to UV rays.

Then, what else affects UPF? It is exposures, thickness, texture, types, etc. Hence, wearing a hat with brim wider than 7.5cm and layers of clothes or clothes that can cover up exposures help to block UV rays effectively.

Polyester is a type of fiber that best blocks UV rays. Wool or silk nylon is the next, and cotton or rayon is known to block UV rays the least. Also, when clothes become wet and see-through, blocking effects of fibers on the surface that reflected visible rays and UV rays reduce.

Now, refer back to how you’ve been using sunscreens. What type do you use, and how much do you apply at a time? Wearing sunscreens do cost time and money, so if you are using it, better do it right.

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