The work, which was carried out by German researchers and is subsequently being presented at the European Congress of Endocrinology in Glasgow, Scotland, could be the latest in a series of consumer scares over the effects of certain chemicals in personal care formulations.
The research team looked at rats exposed to the UV-absorbing chemicals 4MBC, commonly used in a variety of sunscreen and anti-ageing products, together with benzophenone 2 (BP2).
Accordingly, the research team discovered that after treating the rats with 4MBC for 5 days, the levels of thyroid stimulating hormone were significantly raised, while of the other main thyroid hormones, T3 was unchanged and T4 was slightly decreased.
"This change in thyroid hormone levels is typical of the early stages of hypothyroidism," said research leader Professor Josef Köhrle from the Charite University, Berlin.
"In addition to changes in hormonal levels, we also saw a significant increase in the weight of the thyroid glands. These results indicate that 4MBC is a potent inhibitor of the pituitary-thyroid system in rats," he added.
The group also screened human cells for the effect of the UV filter benzophenone 2 (BP2), and found that it inactivated a key enzyme involved in thyroid hormone production.
However, the researchers said that these effects were prevented when there was an adequate amount of iodine in the reaction mixture. This effect was also later replicated this effect in rats.
Professor Köhrle did also stress that these are preliminary studies showing only the effects on animals, adding that the next step will be to determine the effects in humans before any safety conclusions can be drawn.
He also stressed the importance of the continued use of sun care products.
"We need to bear in mind that sunscreens have a beneficial effect in protecting against skin cancer, and so the last thing I'd say to anyone just now is to stop using sunscreens, but less extensive direct sun exposure might be better, too," professor Köhrle added.
MBCs have been found accumulating in environments such as lakes in Switzerland and the research team says it believes that this is down to the increased use of sunscreen products in recent years.
"The work has shown that MBC and BP2 are potent disruptors of the pituitary-thyroid hormonal system in rats. It's early days, but if the same effect is discovered in humans, then we may have to rethink how we protect children and those with existing thyroid problems or those in iodine-deficient areas from sun exposure," professor Köhrle said.
In recent years certain chemicals have come under the microscope and have been linked to increased rates of cancer as well as risks to the reproductive system.
Ingredients such as parabens - widely used as preservatives, phthalates - commonly used as a softner, and aluminium - used in certain deodorants, have brought about criticism from consumer lobby groups worried over scientific reports that suggest these substances could pose risks to human health.