Which type of hair color typically requires a patch test before application?

Permanently formulated hair colors, which often require a patch test, contain chemicals that can potentially cause allergic reactions in some individuals. These products typically use developers that contain hydrogen peroxide or other oxidizing agents that work to lift the natural pigment of the hair and deposit new color. This process can be more intense and invasive, making it essential to ensure that the client's skin does not react adversely to any of the ingredients.

A patch test involves applying a small amount of the product to an inconspicuous area of the skin, usually behind the ear or on the inner elbow, and waiting 24 to 48 hours to check for any signs of irritation or allergy. This precaution helps in minimizing the risk of a severe allergic reaction, which can have significant health implications.

While other hair color types may have their own considerations, they do not typically pose as high a risk for severe allergic reactions, which is why a patch test is primarily emphasized for the application of oxidative tints or permanent colors. Temporary colors, on the other hand, usually do not penetrate the hair shaft and are less likely to cause allergic responses, hence they do not require a patch test.