In most people, an irritant or allergic reaction starts to manifest within 5 or 10 minutes of applying an essential oil, and can be almost instant. Symptoms include .
A small proportion of people may experience skin irritation, allergic reactions, or cross-sensitivity to essential oils. Cross-sensitivity is the potential for an allergic reaction to similar substances (for example, if you are allergic to ragweed, you might also be allergic to chamomile essential oils).
It is prudent to conduct a simple skin test before beginning topical use of a new essential oil.