A full history is needed with the time course of exposures and the onset and duration of the rash. In general, hair dyes induce a type 4 contact allergic dermatitis that presents with itchy, red scaling of the skin lasting up to several days. Phenylenediamine is a common chemical in these products that can cause such a reaction.

Similarly, oral vitamin supplements may also lead to generalized eruptions. Most medicinal grade peanut oils contain very little, if any, peanut protein. If the oil is crudely refined, peanut protein may be present. If so, it could produce a type 1 IgE-dependent reaction that manifests as itchy welts, or urticaria, usually starting within minutes of exposure. She might get an itchy throat when swallowing the preparation. You could do a skin test with the preparation to see if this is the case.

If your patient has persistent hives that keep coming and going, rather than dermatitis, it's unlikely to come from a single contact or a one-time exposure to a vitamin preparation. Rather, you should consider chronic idiopathic urticaria. This condition is usually due to an underlying autoimmune response that persists until the antibody disappears.