I have come to the conclusion that the self tanners do not work as well on the scalp as other parts of the body.
They do work, just not as dark/tan as easily nor do they last the same.
I wonder if it has something to do with fat content.
Anyway they do work the upshot is likely a bit more reapplications and less need to worry that your dome will become darker than your face and neck.
I must use the self tanners because I really hardly tan at all and easily burn. I would never get "good" color on my dome based on sun exposure.
FWIW,
Eric