Australians are being urged to avoid so-called "sunscreen pills" that claim to offer protection from UV rays, with experts warning they are no substitute for actual creams.

A number of US companies manufacture the pills, which are sold to Australians via online vitamin sites.

As Australia swelters through another hot summer we take a look at the manufacturers' claims and what the experts say.

What are the claims?

Manufacturers purport the pills contain antioxidants and natural plant extracts that "protect skin from excessive sun exposure and its harmful effects" and "help limit the damage caused by the sun's rays".

Some rely on a leaf extract native to Central and South America, saying they have been used for "hundreds of years" to "promote various health benefits".

The pills are also claimed to fight premature skin ageing and reduce inflammation.

Are they approved by the regulator?

No.

Australia's Therapeutic Goods Administration (TGA) does not list them on its approved register. Even in the US, where many of the pills are manufactured, they have caught the eye of regulators.

The pills being offered to Australians include one brand that was one of four targeted by the US Food and Drug Administration (FDA) last May for making "misleading" claims.

In a statement, FDA commissioner Scott Gottlieb said:

"These companies … are putting people's health at risk by giving consumers a false sense of security that a dietary supplement could prevent sunburn, reduce early skin aging caused by the sun, or protect from the risks of skin cancer."

"These companies were instructed to correct all violations associated with their products and were advised to review product websites and product labelling to ensure that the claims they are making don't violate federal law."

The companies appear to have since amended some of the claims, with one vitamin site offering the pills including a warning at the bottom of its advertisement that they are not a replacement for topical ointments.

So I should stick with traditional sunscreen?

That's the advice of the Cancer Council.

Spokeswoman Justine Osborne said Australians should rely on the proven "Slip, Slop, Slap, Seek and Slide" approach, and only buy Australian-made sunscreen.

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"There are five messages and five ways to protect your skin … [The pills] are not part of that," she said.

"There's no definitive evidence to let us know that they actually are effective. What we do know is effective is actual sunscreen.

"Australia has very strict regulations and standards, and so if you're buying an Australian sunscreen with an Australian licence number, you know you can trust what's in that sunscreen."

What does the regulator say?

A spokesperson for the TGA urged consumers to "exercise extreme caution" when buying medicine from overseas sites.

"All medicines supplied in Australia, including complementary or 'listed' medicines, such as those indicated to help protect the skin from sun exposure are rigorously monitored for safety," the spokesperson said in a statement.

"Medicines available for purchase over the internet including from overseas-based internet sites may not be subject to the same level of quality control as medicines regulated for sale in Australia by the TGA.

"In some cases [they] contain little or no active ingredients or ingredients different to those as advertised."