The waiting period for re-dying hair depends upon the type of hair dye used initially. If a gentle, semi-permanent hair color that does not contain ammonia peroxide was used, the hair can be dyed within a few days.
Semi-permanent hair dyes that do not contain large amounts of ammonia peroxide are gentler on the hair than ones that do, making them safe to use more often. Permanent hair dyes typically contain ammonia and peroxide. They have a longer-lasting color effect on hair and are harsher to the hair. They typically fade after six to eight weeks and often require touch ups, especially to the hair roots, after this time.
Regardless of the type of hair dye used, frequent dying is likely to damage the hair in some way. The chemicals in the dye strip the natural protective oils from the hair, leaving it vulnerable to damage from blow drying and curling irons. The dye also builds up over time and leads to gummy texture of the hair. This is treated with a clarifying shampoo, which also removes some of the dye pigments, making the color fade more quickly.
If the hair being dyed is not in a good condition, the dye must not be applied until the hair is in a healthier condition, or serious damage to the hair can occur.