Reaction caused by the use of hair colour in mild cases usually only involves dermatitis to the upper eyelids or the rims of the ears. In more severe cases, there may be marked reddening and swelling of the scalp and the face. The eyelids may completely close and the allergic contact dermatitis reaction may become widespread. Severe allergy to PPD can result in contact urticaria and rarely, anaphylaxis.People working with PPD such as hairdressers and film developers may develop dermatitis on their hands; patch testing usually reveals hypersensitivity to PPD. Occupational allergy to PPD has been found in a milk tester whom through laboratory work was in frequent contact with PPD solution. Dermatitis on the hands and occasional spreading to the arms and upper chest occurred. One of the most dangerous applications of PPD is when it is added to henna, a natural dye. When used for temporary tattoos, henna laced with PPD is known as “Black Henna.” Although this is not an approved use for PPD in the United States, some tattoo artists will illegally add the chemical to henna for darker temporary tattoos that dry faster than pure henna tattoos. Because the dye is applied while the PPD is in its oxidation process, its potential as an allergen is increased. Black Henna tattoos often result in a skin reaction similar to a chemical burn, which in turn results in a scar where the skin was tattooed. When added to henna, the concentration of PPD is often much higher than what is approved for use in hair dyes, resulting in a minor to major allergic reaction. Once a person who has been exposed to PPD has an allergic reaction, they may suffer a lifelong sensitivity to the chemical.