The Food and Drug Administration issued warnings Tuesday addressing dietary supplements that claim to protect the public from sun damage.

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"There's no pill or capsule that can replace your sunscreen," the agency wrote. "We've found products purporting to provide protection from the sun that aren't delivering the advertised benefits. Instead they're misleading consumers, and putting people at risk."

The warning letters were aimed at four companies and accused them of "illegally marketing pills and capsules labeled as dietary supplements that make unproven drug claims about protecting consumers from the harms that come from sun exposure without meeting the FDA's standards for safety and effectiveness."

The FDA specifically called out the following products for putting people at risk:

The agency said the companies need to reverse any federal violations associated with their products.

A representative with Napa Valley Bioscience told Time in a statement that their product "is made with ingredients that published clinical studies show protect skin from damage," and is useful for supplemental protection and for users with sensitive skin.

“However, to be abundantly clear: the sun is dangerous, and UV rays damage your skin. We don’t market Sunsafe Rx as a sunscreen, and we certainly don’t tell consumers that they don’t need any other protection from the sun or that they don’t also need to use a topical sunscreen,” the company said. “Everyone should exercise caution when exposed to the sun.”

Skin cancer is the most common form of cancer in the United States, according to the Atlanta-based Centers for Disease Control and Prevention. And one in five Americans are at risk of developing the condition in their lifetime.

The FDA is also researching the effectiveness of current sunscreens on the market as some research has purported some ingredients popular in conventional sunscreens may seep through the skin, though human harm due to this hasn't been concluded.

The AJC published this helpful guide to understanding sunscreens on the market with the help of recent sunscreen data from the Environmental Working Group and Consumer Reports.

Read the full FDA warning at fda.gov.