Sunlight has two types of UV rays that reach your skin: UVA and UVB. They do different damage.

UVB is the shorter wavelength. It's the one that burns you. It hits the outer layer of skin, causes sunburn, tanning, and directly damages DNA in skin cells. It's the main driver of most skin cancers, including melanoma. UVB is stronger in the middle of the day and weaker in the morning and evening.

UVA is the longer wavelength. It doesn't burn, which is why people underrate it. But it penetrates much deeper, into the layer where collagen and elastin live. It's what ages your skin: wrinkles, sagging, loss of firmness, dark spots, and leathery texture over time. UVA also contributes to skin cancer risk. Unlike UVB, UVA is pretty constant all day long and passes through clouds and windows. If you sit by a window in an office, UVA is hitting you.

Sunscreens block these rays in one of two ways. Mineral filters (zinc oxide and titanium dioxide) are metal oxide particles that sit on top of your skin and reflect or absorb UV on the surface. They don't meaningfully enter your bloodstream. Chemical filters are small organic molecules that penetrate into the upper layers of skin, absorb UV, and convert it to heat. They do get absorbed systemically: the FDA has shown that filters like oxybenzone, avobenzone, and octocrylene show up in blood at measurable levels after a single day of normal use, and persist for days after.

For most modern chemical filters (Tinosorb, Mexoryl, Uvinul A Plus), systemic absorption hasn't shown clinical harm. For the older US chemical filters (oxybenzone, octinoxate, avobenzone, octocrylene), that's where the fertility and hormone concerns originate. If you're pregnant, trying to conceive, breastfeeding, or just risk-averse, mineral is the default safer choice. Otherwise, modern chemical filters are fine and cosmetically much nicer.

Flip the bottle over. Look at the active ingredients list.

Buy it if you see any of these:

• Tinosorb S (bemotrizinol) or Tinosorb M (bisoctrizole)
• Mexoryl SX, Mexoryl XL, or Mexoryl 400
• Uvinul A Plus (diethylamino hydroxybenzoyl hexyl benzoate)
• Uvinul T 150 (ethylhexyl triazone)
• Zinc oxide at 10% or higher (ideally combined with titanium dioxide)

These are the modern filters. They cover UVA and UVB, stay stable in sunlight, and don't break down on your face over the course of a day.

Put it back if the active ingredients are only:

• Avobenzone + octinoxate + octisalate + homosalate + octocrylene + oxybenzone

This is the standard US chemical sunscreen formula. It works for UVB (you won't burn), but UVA coverage is weaker and avobenzone degrades in sunlight. It's also the formula linked to the fertility concerns. If you're in the US and this is all you can find, go mineral (zinc oxide).

Also check:

• SPF 50 or higher on the front
• PA++++ (if it's an Asian sunscreen) or a UVA in a circle logo (European)
• "Broad spectrum" is the bare minimum, not a guarantee of good UVA coverage