The word you seek is pilar.
Merriam-Webster defines the word pilar to mean:
of or relating to the hair or a hair
Another seemingly less common term is crinal:
of or relating to the hair
I say "less common" having observed the following Ngram:
Interestingly, there may be a slight difference in meaning between the two, indicated in the pages of James Cowles Prichard's Researches Into the Physical History of Mankind, Volume 1:
For the sake of facilitating comparison, I shall divide the hair into crinal and pilar, terming crinal that of the head, beard, &c., and pilar that which grows upon the trunk, particularly on the breast and on the limbs.
As pointed out in the comments, however, hair itself cannot suffer from a disorder as it is not living.
Yes, English has at least two adjectives for hair, and they are pilar and crinal.
P.S. I used the Reverse Dictionary to find these terms. You might find it helpful in future.