each with its own impacts on your body and the environment.

With so many options,

how do you choose which sunscreen is best for you?

To answer that question,

we first have to understand how sunscreens work.

Sunlight is composed of electromagnetic waves

and is our primary source of ultraviolet radiation,

which has a shorter wavelength than visible light and carries more energy.

UVA,

UVB,

and UVC are classified according to their wavelengths.

Short wavelength UVC never reaches the Earth's surface,

but UVB and UVA do.

Medium wavelength UVB rays can enter the skin's superficial layers

and long length UVA rays can penetrate into the deeper layers.

UVB in small amounts actually helps us make vitamin D,

which enables our bodies to build and maintain strong bones.

However, prolonged exposure to UVA and UVB can damage DNA,

age your skin,

and promote the development of potentially deadly skin cancer.

Sunscreen protects your skin either physically by deflecting UV rays

with an inorganic blocker like zinc oxide or titanium dioxide,

or chemically by using carbon-based compounds to absorb UV photons

that are then harmlessly dissipated as heat.

So, what differentiates one sunscreen from another?

When we choose a sunscreen,

we can compare application method,

the SPF,

and the active ingredients.

Sprays can be convenient to put on, especially when you're wet,

but a recent study found that most people don't apply a thick enough layer

to get full protection.

And the possible health risks of inhaling sunscreen compounds from a spray cloud

might make you consider reaching for that bottle of lotion instead.

Opt for a sunscreen with an SPF of at least 15, although 30 is better.

SPF is a nonlinear scale of how much UVB radiation is needed

to give protected skin a sunburn.

SPF 15 does a pretty good job by blocking 93% of UVB rays.

You get a slight increase as SPF goes up,

with SPF 30 blocking 97%,

and 50 blocking 98%.

SPF is based on the quantity of solar exposure.

So how much time you have before you start to burn

really depends on a long list of factors,

including your genetics,

and when, where, and how you spend your time in the sun.

Even though US marketed sunscreens have been deemed safe by the FDA,

scientists are still researching the effects of many active ingredients

on the human body.

So if you're worried about potential irritants,

look for mineral-based formulas with zinc oxide or titanium dioxide.

Even though they may go on a bit thick at first,

they're less irritating than carbon-based chemical sunscreens.

These mineral-based sunscreens are preferential for the environment, too.

If you plan on catching rays while splashing in a river or the ocean,

keep in mind that carbon-based chemical sunscreens

can harm marine life.

Take coral reefs for example.

Although they cover less than 1% of the Earth's underwater surface,

they're home to nearly 25% of all fish species,

making them the most diverse and productive marine ecosystems.

Research shows that carbon-based chemical sunscreen ingredients,

like oxybenzone, butylparaben, octinoxate, and 4MBC

contribute to a stress condition called coral bleaching in corals,

which are living creatures.

Exposure to these organic compounds

results in the death of the coral's symbiotic algae.

In addition to providing a reliable food source,

these algae give coral their brilliant rainbow of colors.

Without them, corals turn a bleached white

and are susceptible to disease and possibly death.

And once the coral dies,

the entire reef ecosystem is not far behind.

So you're now ready to make an informed choice when picking out your next sunscreen.

SPF is clearly labeled on the front.

On the back under "active ingredients,"

you can find whether zinc oxide,

titanium dioxide,

and those coral-harming components are present.

Taking a bit more time to check can be well worth it

for both you and the environment.