How To Apply Sunscreen Properly Explained By A Dermatologist

Hello, I'm Dr. Ji-in Jung, a dermatologist. Many people find applying sunscreen bothersome due to its sticky and heavy feel. You know you should apply sunscreen for skin protection, but do you know why it's so important? Today, I'll discuss the necessity of sunscreen and its proper use in detail.

Ultraviolet (UV) rays reaching Earth can be broadly divided into UVA and UVB. Generally, when people think of UV rays, they might recall sunburn, blemishes, melasma, and in severe cases, skin cancer. UVB primarily influences these symptoms. The UVB protection factor is indicated by the SPF number on cosmetics.

However, we also need to pay attention to UVA. The UVA protection factor is indicated by PA+ or PA++ on cosmetics. While UVA is about 1/1000 as effective at causing erythema as UVB, the amount reaching the Earth's surface is 8 to 10 times greater. Additionally, UVA, being a long wavelength, penetrates deep into the skin, causing photoaging such as blood vessel dilation, photosensitive diseases, and deep wrinkles, and can also be a cause of melasma and blemishes.

Therefore, it is advisable to choose a sunscreen product that adequately blocks both UVA and UVB.

To prevent pigmentary disorders like melasma and blemishes, or photoaging, it is recommended to choose a product with at least SPF 15 and PA++ for daily life. In special situations, such as after laser procedures, SPF 30 or higher may be recommended.

Most commercially available sunscreens contain an appropriate blend of physical and chemical blockers.

• Physical blockers (mineral sunscreen)

  • Are not absorbed by the skin and create a physical coating that reflects UV rays.
  • Are stable as they do not change due to UV exposure.
  • Their effect is relatively weaker and they are prone to leaving a white cast.
  • While recent products have improved this, a somewhat stiff feeling may remain.
  • Excessively strong cleansing to remove this stiff feeling can damage the skin, making it more vulnerable to irritation.
  • They are superior in terms of overall safety. Zinc components are primarily used.

• Chemical blockers (organic sunscreen)

  • Absorb UV rays within the skin and neutralize their effects.
  • Feel good on the skin and have less white cast, making them convenient to use.
  • Have the advantage of effectively blocking UV rays.
  • However, they can decompose due to UV exposure and may cause allergies during skin absorption.
  • Some ingredients are known as hormone disruptors, and there are reports that they can negatively impact marine ecosystems if swimming in the sea or rivers.

Sunscreen should be applied every day, all year round. People often don't apply sunscreen when mostly indoors or on cloudy days, but windows block only about 30% of UV rays, and seawater blocks about 50% at a depth of 50cm; most UV rays pass through. Therefore, it's good to make a habit of thoroughly applying sunscreen before going out in the morning.

Sunscreen is typically applied after completing basic skincare, just before leaving for work. Since it contains many oily ingredients, it's best to apply it as the last step of skincare, before makeup.

Correct amount and application method

Applying about one and a half finger-lengths of sunscreen to the entire face is generally appropriate. The actual amount applied may be more than you think. Squeeze out about one finger-length of product, place a dollop on the forehead, both cheeks, and chin, then tap it gently with your fingertips to spread it. It's especially good to apply it carefully to the eye area and bridge of the nose, which are often neglected. These areas tend to develop the most blemishes. You should reapply it several times with sufficient time in between to ensure even coverage.

Also, it takes about 30 minutes for sunscreen to settle on the skin and spread evenly. Therefore, applying it about 30 minutes before going out, rather than just before, can be helpful.

The effectiveness of sunscreen largely depends on the amount applied. According to one study, people tend to use only about 1/4 of the recommended amount (2mg per square centimeter). In this case, even if an SPF 15 product is used, the actual effect might only be equivalent to SPF 2. This is also true for products with high SPF ratings.

Some people think that applying multiple layers of color cosmetics containing sunscreen adds up their SPF, but this is not the case. It's more important to reapply several times than to apply many different products at once.

If possible, it's best to reapply every 2 hours, but if that's not feasible, touching up with powder containing sunscreen ingredients is also a good method. However, spray-on sunscreens that are directly sprayed on the face are not recommended as they can be inhaled into the respiratory system.