Heat kills sunscreen faster than light.

Yes. Leaving sunscreen in a hot car or in direct sunlight will make it expire faster. Heat is the main enemy, not UV exposure.

Sunscreen’s active ingredients (both chemical and mineral) break down at high temperatures. A car can easily hit 140°F inside on a summer day. That’s enough to degrade the formula in weeks, sometimes days. Direct sunlight also adds heat, but the bigger risk is the temperature spike.

You can still use it if it hasn’t changed texture or smell, but don’t trust it for a beach day. If it feels watery, grainy, or smells weird, toss it.

Keep sunscreen in your bag, not the glovebox. Your skin will thank you.