Coconut is a tree nut and can cause allergic reactions such as occurs with Brazil nuts, Cashew nuts and Hazelnuts. We used to think it was quite a rare food allergy and was not often reported as problematic. But prevalences seem to on the increase and more people report oral allergic reactions and rashes when consuming Coconut in Asian foods and exotic drinks. Coconut milk is now readily available in health stores and supermarkets and more people drink Coconut milk than ever before. Sensitisation may occur in babies and young children when coconut oil is applied to the skin as a moisturiser. Coconut allergy testing can be done on the skin (Skin Prick Test) and on a blood sample (RAST test). See Wikipedia for more information on Coconuts.
