London: Do you lather yourself with sunscreen to keep out that tanning? Beware!

According to a new study, sunscreens are likely to impair sperm cell function, acting as a male contraceptive and lower a man's chances of parenthood.

The findings of the study showed that many ultra-violet (UV) filtering chemicals commonly used in sunscreens interfere with the function of human sperm cells, and some mimic the effect of the female hormone progesterone.

Sunscreen impairs sperm function by seeping through the skin and into the rest of the body, the researchers explained.

UV-filtering chemicals were found in almost all urine samples and some blood samples.

"These results are of concern and might explain in part why unexplained infertility is so prevalent," said one of the researchers Niels Skakkebaek, professor at the University of Copenhagen in Denmark.

To examine how UV-filtering chemicals affect healthy sperm, the team tested 29 of the 31 UV filters allowed in sunscreens on healthy human sperm cells, in a buffer solution that resembled the conditions in female fallopian tubes.

The team concentrated on calcium signalling - particularly the sperm-specific calcium ion channel called CatSper, which binds to the female hormone progesterone to control sperm cell fertilisation functions like sperm motility.

The results revealed that 45 percent, of the 29 UV filters tested in the study interfered with the normal functioning of the sperm cell. 

Also, 13 UV filters triggered a surge in the movement of calcium ions within sperm cells during binding with progesterone.

"This effect began at very low doses of the chemicals, below the levels of some UV filters found in people after whole-body application of sunscreens," Skakkebaek said.

The study suggests that regulatory agencies should have a closer look at the effects of UV filters on fertility before approval, the researchers concluded.

Results of the study were presented at the ongoing Endocrine Society's 98th annual meeting in Boston, US.