The curlier your hair is, the less often you should wash it. However, you should never let it go for more than 10 days. The reason for this is because both normal hair fungus and tinea (ringworm) fungus only need two weeks (14 days) to grow out of control. You may not be able to help having a little dandruff, or even keep yourself from catching ringworm, but you can reduce your chances with regular washing.
Curlier hair has a thinner cuticle than straight hair, and because of its curliness, moisture in oils and sweat is held closer to the head. So the hair shaft does not get heavier from a few day’s worth of accumulation. Your hair actually needs those natural oils to protect it and your scalp.
You should make an exception however, if you are swimming in heavily chlorinated or salt water daily or almost daily. In this case, you should wash your hair with a very gentle shampoo, preferably made for your activity. You should also avoid too much detangling conditioner, as daily exposure to water softens your hair enough. You don’t want to overdo it.
Rather than detangling, the frequent washer should slicken. Slickening oils like pure argan oil, and virgin coconut oil make the hair shaft slick without being too alkaline and therefore breaking down the hair’s structure.