Sun Screens

The EM spectrum goes from gamma rays with (10 $^{-} 12$ m $λ$ ) to radio waves (100m $λ$ ).
Visible spectrum is 400nm to 700nm (blue to red).
Ultraviolet (UV) light is 100nm to 400nm. This is divided into 3 bands:

Band	Wavelength	Impact
UV-A	320nm-400nm	- Penetrates deep into the skin - Causes skin cancer, ageing, wrinkles, dark spots - Goes through glass and clouds
UV-B	280nm-320nm	- Doesn't penetrate as deep - Causes skin cancer. - Doesnt go through glass/clouds.
UV-C	100nm-280nm	This is completely absorbed by ozone layer so no need to worry about it.

So, we need protection for UV-A and UV-B.
- UV-A protection needed even in office etc. since it goes through glasses and clouds.

NOTE: Check INCIDecoder - Decode your skincare ingredients for ingredients and their impact.
Ideally mineral based:
- Zinc oxide is the best sunscreen wrt protection, stability, safety, environmental impact. But it leaves a white cast.
- Titanium oxide is not as powerful as zinc oxide.
Chemical based:
- These leave no cast, but have low stability. And might be environmentally unsafe.
Ingredients to avoid:
- benzophenone-3, oxybenzone, octinoxate, and octocrylene
- These have bad environmental impact, and some are shown to penetrate into the body, impacting blood, urine, breast milk etc.