Covering the penis, scrotum, and vulva with petroleum jelly may offer some added protection if the coloring drips before the dye can be washed off with water. To minimize potential harsh effects, protect the sensitive genital area with a washcloth. Folks with soft pubic hair may not want to use bleach because the texture of the hair will change. Rinse only with water so as not to increase the chance of irritation. If you and your girlfriend have any more questions about using a specific hair color product, try contacting the manufacturer.
Many companies provide a toll free customer service number on their packaging.