It's a common belief that dirty hair grows faster. There's no scientific evidence to support this claim. However, there are a few possible explanations for why it seems like dirty hair grows faster. One reason may be that when hair is clean, it's more visible against the scalp. This makes it appear shorter than dirty hair, which can make it seem like it's growing slower. Additionally, scalp oils and product buildup can weigh down hair and make it appear thinner. When you wash your hair, these things are removed and your strands look fuller and healthier. This can also make it seem like your hair is growing faster. Of course, everyone's hair grows at different rates. Some people may find that their hair grows faster when it's dirty, while others may notice the opposite. The best way to know what works for you is to experiment with different washing schedules and see how your hair responds.