Chemicals in sunscreen may get absorbed into the bloodstream in amounts that exceed safe levels, research suggests.
Sunscreen is known to ward off UV damage that can lead to skin cancer, however, many are increasingly concerned about the chemicals in the formulations.
In a study by the US Food and Drug Administration (FDA), 48 volunteers applied one of four unnamed products all over their body 13 times across four days.
After a single application, blood tests revealed six chemicals were present at levels exceeding the FDA’s safe threshold of 0.5 ng/mL.
Chemical-based sunscreens contain filters that absorb UV radiation, warding off skin damage.
Although effective, their safety is under increasing scrutiny.
To learn more, the volunteers were told to apply either a lotion, aerosol spray, non-aerosol spray or pump spray sunscreen to 75% of their body.
Blood tests looked at the concentrations of six chemicals - avobenzone, oxybenzone, octocrylene, homosalate, octisalate and octinoxate.
Results, published in the journal JAMA, reveal all of the chemicals exceeded safe levels in at least one of the sunscreen formulations.
This was most pronounced with oxybenzone, which reached 258.1ng/mL following the lotion application and 180.1ng/mL with the aerosol spray.
Avobenzone was below safe levels after using the aerosol (3.5ng/mL), non-aerosol (3.5ng/mL) and pump (3.3ng/mL) sprays.
Yet, it reached 7.1ng/mL after applying the lotion.
The concentrations also increased every day, “suggesting accumulation within the blood”.
At day seven, all the chemicals remained above the FDA’s threshold, with homosalate and oxybenzone lingering at day 21.
Skin evaluations revealed the ingredients were also “on the surface”.
Writing in a linked editorial, scientists from the universities of Texas in Austin and California in San Fransisco said the skin may act as a “depot for ongoing absorption”, even after the sunscreen is no longer applied.
No immediate safety concerns came to light, with 14 of the participants developing a rash.
Nonetheless, oxybenzone and homosalate have been linked to hormonal disruption.
“Multiple” chemicals lack safety data when it comes to cancer, developmental and reproductive risks, the FDA authors wrote.
They stress, however, the results “do not indicate individuals should refrain from the use of sunscreen” ahead of further research.
The linked editorial added the benefits of sunscreen may outweigh any risks, which could alter according to skin type and the frequency of application.
For now, “sunscreen should continue to be an essential part of UV safety”, it added.
Professor Antony Young, from King’s College London, said: “Overall, there is increasing evidence sunscreens applied to the skin can enter into the circulation.
“The problem is we do not know what the health effects of this are.
“From limited data there is no evidence long term sunscreen use has any effect on mortality.
“This would not be an easy area to research on humans for many reasons, not least of which is that sunscreens contain a cocktail of UV filters.
“If used correctly, sunscreens are an excellent way to prevent the short and long term adverse effects of solar UV rays.”
Professor Rob Chilcott, from the University of Hertfordshire, added: “It is also worth considering the study was performed under conditions which provided a worst-case scenario in terms of the amount of sunscreen applied to the skin.
“In reality, the amount of sunscreen applied by users will likely be lower and will be subject to continual loss between each application."