The trap of "it's cloudy, so I'll skip it today"
Do you decide whether to wear sunscreen based on the morning sky? Then today too, your skin is quietly aging. UV rays come down at nearly the same intensity whether the sky is blue, gray, or raining.
UVA and UVB have different personalities
- UVB: Short wavelength, acts on the epidermis → direct cause of sunburn and melasma. Largely blocked by clouds and glass.
- UVA: Long wavelength, penetrates into the dermis → main driver of collagen destruction, photoaging, and loss of elasticity. Passes almost freely through clouds and ordinary glass.
In other words, UVA is what ages your skin the most over time, and it doesn't care about the weather.
Thin clouds = 80% UV transmission
According to WHO UV Index reports, on average more than 80% of UVA passes through a thin layer of clouds. Light fog and overcast skies can even scatter UV rays, spreading them more evenly across your skin.
Car side windows also fail to block UVA. That's why people who drive or commute by bus often develop asymmetric pigmentation on one side of the face.
UV-defenseless self-check
- You often skip sunscreen on cloudy days or in winter
- You work indoors so you feel it doesn't matter
- You drive or commute by bus more than an hour a day
Action plan
Step 1. Everyday application
- Make it the fixed last step of your skincare
- 1g for the face (about two 500-won coins)
- Extend to ears, neck, and back of the hands
Step 2. Reapplication routine
- Use sun sticks or cushions to reapply over makeup
- Every 2–3 hours, and once more before going out for an appointment
- Thin layers, applied more often
Closing thoughts
Sunscreen isn't just a summer cream — it's the final step of skincare, 365 days a year. Cloudy, indoors, or winter — 1g every morning. Ten years from now, your face will tell you the difference.