have you ever wondered how sunscreen works? This is a quite funny explanation.
When you look in the mirror you see a uniform skin color in visible light, but the sun sees something else: little freckles, which are little patches of melanin - or skin pigment. These are the signs of ageing and sun damage that we can’t ordinarily see.
Using a special camera, the UV reflected from people's skin can be made visible. With healthy skin, there is a uniform, high reflection and the skin looks smooth. No sun damage. With aging, the skin looks more freckled, and with really damaged skin the skin reflects even less and has these absorption spots. If there is more damage, there can be a start of skin cancer.
But then, there is sunscreen, and how does this work? For example, glass blocks UV light, but we cannot wear glass on our skin or need to stay indoors all the time. Sunscreen does something similar to glass: it absorbs the UV light so that it does not reach the skin. But with no reflection at all, the people with sunscreen look like they applied black make-up to their faces, which is pretty funny.