How Often Should I Wash My Hair?
It all depends on a number of factors. One is your skin type, which is determined by genetics, lifestyle and age. Your scalp's skin type tends to correlate with your face's skin type, specifically your t-zone, says Mirmirani. So, if your forehead, nose and chin tend toward dry, then your scalp probably is, too, and a moisturizing shampoo can help—but stick to once or twice a week to avoid over-drying the scalp. If you have an oily T-zone and scalp, you can shampoo more often (say, three times a week).
Beyond skin type, consider your hair's texture, length and density to help figure out how long the intervals should be between washing. If you have shorter, straighter, more dense hair, says Mirmirani, you could wash it every day (though you definitely don't need to), because sebum (aka natural oils) tends to spread more quickly in these cases. People with longer, thinner or heat- or color-treated hair should shampoo less frequently, she says, since hair with those attributes tends not to tolerate shampooing as well (your hair may feel brittle, or look dull). For most textured hair, Mirmirani says, shampooing more than once a week can really dry out the hair and the scalp.
And highly active people needn't overcompensate with extra washing: leaving sweat on your scalp after a tough workout isn't going to damage it in any way. If it's smelly, though, Mirmirani says try dry shampoo. Another option is just rinsing; this can be especially useful if your workout involves swimming in a chlorinated pool.