The duration that beard hair dye lasts can vary depending on the specific product, the color, and individual factors such as hair type, lifestyle, and maintenance routine. Generally, semi-permanent hair dyes can last anywhere from a few days to a couple of weeks, while permanent hair dyes can last up to 6 weeks or longer.
It's important to note that beard hair may grow quickly, which can result in noticeable roots and fading of the dye over time. Also, factors such as frequent washing, exposure to sunlight, and using harsh hair products can cause the dye to fade faster. Therefore, proper maintenance, including using a color-safe shampoo and avoiding excessive washing, can help extend the life of the beard hair dye.