I had greasy teenage hair; back in the day (big, freezing cold house, no central heating, limited hot water) it was quite usual to only shower/wash hair a couple of times a week. I used to buy "shampoo for greasy hair".
ds2 has greasy teenage hair and a reluctance to shower daily (hmm). His hair looks lovely when it's just been washed, but starts to look rather lank and limp within about 6-8 hours; looks well past its best the next day, and truly grim on 3rd (and subsequent!) days.
I looked in Boots for "shampoo for greasy hair", but it appears such a product no longer exists.
Any suggestions?