The ultraviolet (UV) filtering ingredients in sunscreen products interfere with the normal function of human sperm when applied to a sperm-containing solution in the lab.
Researchers tested 29 of the 31 UV filters approved for use in sunscreens in Europe or the USA to see whether they interfered with calcium ion signaling in sperm, a process that is important for normal function and critical for successful fertilisation.
The UV filters were assessed using sperm cells obtained from the semen of healthy volunteers and placed in a buffer solution designed to simulate conditions in the fallopian tube. At a conference of the US Endocrine Society, the authors reported that 13 of the UV filters tested caused an inappropriate surge in calcium ions.
'These effects began at very low doses of the chemicals, below the levels of some UV filters found in people after whole-body application of sunscreens,' said lead author Professor Niels Skakkebaek, from the University of Copenhagen.
The study also reported that nine of the 13 UV filters that induced an influx in calcium ion directly activated the sperm-specific calcium ion channel known as CatSper, thereby mimicking the effects of the female hormone progesterone. The study notes that 'some' of the UV filters affected sperm motility and viability but does not give further detail.
According to the study authors, previous research has shown that UV filters are rapidly absorbed through the skin and can be retrieved from blood and urine samples from healthy male volunteers who have used them.
Professor Skakkebaek said that the surge in calcium ions induced by UV filters might suggest these chemicals are 'endocrine disruptors,' and could 'explain in part why unexplained infertility is so prevalent.'
The authors say that clinical studies are now needed to see whether sunscreen has any effect on human fertility. They suggest that 'regulatory agencies should have a closer look at the effects of UV filters on fertility before approval.'
The study has not yet been published in a peer-reviewed journal.