Vaseline can be harmful to your hair if used in excess or not rinsed out properly. It can cause buildup on the scalp and hair, leading to greasy hair, scalp irritation, and flaking. Additionally, Vaseline is a petroleum product, which could dry out the hair, making it brittle and prone to breakage. If you are using Vaseline on your hair, it is important to rinse it out thoroughly and use it in moderation.