How personal care products trigger skin allergy decoded

New York : Researchers have uncovered the mechanism by which chemicals present in consumer products like lotions and perfumes trigger skin allergy, an advance that may lead to new ways to treat the condition.

According to the study, published in the journal Science Immunology, skin allergy may be triggered by chemicals in consumer products due to the way they displace natural fat-like molecules -- called lipids -- in skin cells.

The researchers, including those from Columbia University in the US, said an allergic reaction begins when the immune system's T cells recognise a chemical as foreign.

But they added that the T cells do not directly recognise small chemicals since these compounds needing to undergo a modification with larger proteins to make themselves visible to T cells.

"However, many small compounds in skin care products that trigger allergic contact dermatitis lack the chemical groups needed for this reaction to occur," said study co-author Annemieke de Jong from Columbia University.

"These small chemicals should be invisible to T cells, but they're not," de Jong added. The scientists suspected that CD1a -- a molecule abundant on the immune cells in the skin's outer layer called Langerhans cells -- may be responsible for making the chemicals visible to T cells.

In the current study, the researchers found that the chemicals known to trigger allergic contact dermatitis (ACD) were able to bind to CD1a molecules on the surface of Langerhans cells and activate T cells.

Chemicals like balsam of Peru, and farnesol, which are found in many personal care products, such as skin creams, toothpaste, and fragrances, were found to trigger ACD through this mechanism.

The researchers identified the chemicals benzyl benzoate and benzyl cinnamate present in balsam of Peru as the causative agents for the reaction, and overall they found more than a dozen small chemicals which activated T cells through CD1a.

"Our work shows how these chemicals can activate T cells in tissue culture, but we have to be cautious about claiming that this is definitively how it works in allergic patients," de Jong said.

Further analysis of one of the chemicals, farnesol, revealed that when it forms a complex with CD1a, the compound kicks out naturally occurring human lipids, making CD1a more visible to T cells, and leading to T cell activation.

"The study does pave the way for follow up studies to confirm the mechanism in allergic patients and design inhibitors of the response," de Jong added.