Skin sensitisation and preservatives: how in vitro tests can contribute to more human-relevant safety evaluations
Preservatives in cosmetics are well known skin sensitisers and a common cause of allergic contact dermatitis. Annex V of Cosmetics Regulation EC 1223/2009 lists 57 preservatives approved for use in cosmetic products in Europe, with maximum allowable concentrations, but much of the available safety information depends on historical animal data with limited human relevance.
Global industry efforts have resulted in the development of 3 OECD-approved in vitro tests for skin sensitisation, and new non-regulatory methods can be used to build a weight of evidence to demonstrate the safety of preservatives, including a prediction of potency. The tests provide a route for the re-evaluation of safe limits with increased relevance for humans, and assessment of proposed new preservatives for Annex V without the use of animals.
WHAT IS SKIN SENSITISATION?
Skin sensitisation is an allergic response following skin contact with a substance. It’s a complex cascade that was relatively poorly understood until recently, which held back progress in the development of in vitro tests. However, the Adverse Outcome Pathway (AOP) has now been described, consisting of a series of key events (Figure 1).
WHY SKIN SENSITISATION TESTING IS SO IMPORTANT
In a recent study of more than 12,000 people in Europe, 31.8% reported a skin reaction to a cosmetic product within the last year, with 37% actively avoiding skincare products known to cause a reaction (1). While many of these were thought to be irritation responses, a significant proportion may be attributed to allergy and up to 10% of dermatology patients who are patch tested in the UK are thought to have at least one allergy to cosmetic products or their ingredients (2).
As skin sensitisation is a permanent condition involving our immune response, it is much more serious than irritation and forms an essential part of cosm ...