This is a common contraindication, as some clients may be allergic to or have sensitivity to certain products, essential or carrier oils. An allergic reaction is the immune system’s reaction to allergens which can be in a particular oil or product for a client and, if used, could cause a reaction such as skin irritation, rash, headaches, or even burning sensations in the eyes or throat.

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Irritation and allergic reactions - Tisserand Institute

If a client has never had an aromatherapy massage before, they should have a patch test carried out at least 24 hours prior to the massage. A new blend can be patch tested before a treatment for the client, as they will usually react straight away if allergic.