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Purple shampoo is often used to help brighten blonde and gray hair. It can help neutralize orange, yellow, or green tones, since purple is opposite these colors on the color wheel. This type of shampoo should not be used every day, since it can actually cause very light hair to turn purple. Instead, most professionals recommend using it about once each week.
Along with the cleaning and moisturizing agents found in most other shampoos, purple shampoo has a pigment added. This pigment is usually a violet color, but it can sometimes be more of a blue. Purple conditioners and other purple hair-care products are also available.
Purple shampoo is most often used for blonde hair, although some individuals with gray hair use it as well. This type of shampoo typically works best on chemically treated hair, like bleached hair, since it is more porous. Some of these shampoos may also work on natural blonde hair.
This type of shampoo is commonly used to remove unwanted pigments left in dyed hair. Certain types of hair dyes can leave brassy or yellow tones in blonde hair, giving it an unwanted hue that can increase over time. When the purple color is put on the hair, it will neutralize the unwanted colors.
Blonde hair also has a habit of turning greenish after exposure to the chlorinated water in some swimming pools. The chlorine can oxidize copper found in some algaecides, turning it green. This color can sometimes seep into more porous hair, and it's especially obvious in people who have light blonde hair. Shampoo with a purple coloring can often counteract this and return the hair to its more natural color.
Using purple shampoo every day can actually cause hair to turn purple, however, so it should really only be used every few days or once a week. Leaving the shampoo on the hair for too long can also give the hair a purple tone. Any unwanted purple color will typically fade with time, but to return the hair to its normal color more quickly, deep cleansing or clarifying shampoos can be used. A shampoo for blonde hair that has yellow pigments in it may also help neutralize any lingering color.