You don’t need the blazing hot temperatures of a heat wave to get sunburned — in fact, temperatures have nothing to do with it. Surprised? What you don’t know about sunburns could literally be hurting you, so let’s lay it all out there.

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A sunburn isn’t caused by the sun’s heat

A sunburn is a radiation burn. It’s your body’s inflammatory response to damage to your skin cells caused by ultraviolet rays. That inflammation causes your blood vessels to dilate, which causes the swelling, redness and warmth you feel. 

While it may be hotter outside when the UV index is high, that index is not a measure of heat. So it can be a cold, windy day in the Colorado mountains and a high UV index can leave you with a painful sunburn.

(MORE: What is the UV Index?)

Clouds won’t save you

UVA rays (which have the longest wavelength and penetrate deeper layers of your skin), pierce right through clouds, rain and fog.  

The Skin Cancer Foundation points out that up to 80% of UVA rays can penetrate light, thin cloud cover. Clouds may even boost UV levels because of scattering, says the World Health Organization, so their advice? “Don't be fooled by an overcast day or a cool breeze!”

The beach and water are sneaky

When you’re sitting out on the beach, sand can reflect about 15% of UV rays right back at you. So you can burn even if you’re under an umbrella. The ocean or water in your pool can reflect about 10% of UV, according to the WHO, and because the water keeps you feeling cool, it can mask a sunburn.

For winter sport lovers, fresh snow can almost double your UV exposure. Higher altitudes also increase UV levels — skier’s sunburn, anyone?

Your medicine could betray you

Common medications, both prescription and over-the-counter, can increase your sun sensitivity and make you burn faster. The U.S. Food and Drug Administration has a list that includes:

• NSAIDs: ibuprofen, naproxen and others
• Antibiotics: ciprofloxacin, tetracycline, doxycycline
• Blood pressure diuretics: furosemide, thiazides
• Acne medications: tretinoin, isotretinoin, benzoyl peroxide
• Skin care products with retinol, alpha-hydroxy acids

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The FDA says not all people using these kinds of medications will have a reaction.

Melanin is not sunscreen

While people with darker skin burn less easily, we’re not immune to sunburns. The darkest skin only offers the natural protection of about SPF 13 at the most, say researchers. Sunburns can also be harder to see on darker skin, so damage can go unnoticed and skin cancer in people of color is often found later, when it’s deadlier.

So no matter the temperature, clouds or skin tone, take measures to protect your skin and your health. Apply sunscreen with an SPF of 30 or higher, reapply every two hours, seek shade when the sun is at its strongest, and check the labels on your medications.