Generally, this will depend on many factors including: - your Unique Hair Profile (e.g. scalp condition & hair type) - the climate where you live (incl. seasonal changes) - your activity level - the amount you sweat (either due to your activity level &/or climate) For example, someone with an oily scalp type, straight hair, warm climate, high activity level and who sweats a lot is going to want to wash their hair much more frequently (every 1-2 days) than someone with a dry scalp types, curly hair, cold climate, low activity level and who sweats minimally (4-5+ days). Many people find it is best to wash hair on the days they work out due to increased perspiration, but others find that using a scalp toner in between washes is good enough. It is ultimately up to you and your own hair goals. You can try washing your hair at different frequencies based on your profile and activities to find what works best for you!