Sunscreen is not a 'cosmetic', it's skin insurance^^~

80% of skin aging is due to UV rays, and sunscreen is the cheapest and most effective anti-aging insurance to prevent this.
In other words, 80% of skin aging is caused by ultraviolet rays (photoaging) rather than age spots.

This is why applying sunscreen daily is the most effective investment you can make to prevent loss of elasticity and freckles.
Long-wave UV rays, regardless of whether it's sunny or cloudy, penetrate through glass windows and reach the dermis layer, destroying collagen even indoors. They don't cause burns, but they gradually accumulate and become the main cause of deep wrinkles and loss of elasticity.
To see the effects of sunscreen, regardless of whether you go out or not, the answer is to apply a generous amount of sunscreen, about the size of one knuckle of your index finger, as the final step of basic skin care after washing your face in the morning.

I guess it's true since I heard it in a lecture.