Shampoos and Conditioners are Frequent Causes of Common Skin Problem

Considerably more people than previously believed are allergic to the most common fragrance ingredient used in shampoos, conditioners and soap. In a study, over 5 percent of those who underwent patch testing were allergic to the air oxidized form of the fragrance ingredient linalool.
Linalool is found in 60 to 80 percent of perfumed hygiene products, soap and household cleaning agents that can be bought in the supermarket, so it can be difficult for people who are allergic to avoid these products.
In the study, oxidized linalool was added at patch testing for more than 3,000 patients who wanted to find out what was causing their eczema. Between 5 percent and 7 percent proved to be allergic.

Sources:
Eurekalert March 27, 2009
Contact Dermatitis January 2009