Lynn is absolutely correct, there is a definite correlation between thyroid and hair, especially with hair loss. Any sudden metabolic changes will cause hair to shed, as it is one of the fastest growing cells going. So thyroid, adrenals, liver are all connected one way or another to healthy hair. Oh and a note on Armour - it has to be taken 2x a day to keep levels of T3/T4 steady.
Lack of Vit A and minerals leads to hair brittleness. Hair depends on protein for growth, fasting or low-protein diets will slow down hair growth. Hair tends to grow faster as the moon waxes, slows down as it wanes, so get your haircut done after the full moon if you want it to last. :) Take a full-spectrum B complex occasonally, good hair needs B vits.
To keep the follicles clean and healthy is the main objective to beautiful, full hair. There are many ways to do this. Keep your diet mucous-free with plenty of good EFA oils and dark green veggies and whole grains are the basics. If you ever notice those tiny pore bumps on the back of your arms, that is due to EFA insufficiency. That kind of clogging is happening to your head hair too.
Keep the circulation up by doing the detox bath. The niacin will cause the scalp to flush.
I've heard of rosemary and lavendar and peppermint teas being used. Thyme sounds like a good idea, it hsa positive actions on the skin and circulation.
Massage helps, including a kind of metal stamp made out of a bunch of needles like a toothbrush to prick the skin and increase circulation - that always seemed way too much to me! LOL! Acupuncturists sell them. Good for premature balding. At least massage while washing the hair.
For hair that's already grown, to keep it healthy you must protect it (hot oil treatments, leave-in sun protector) by not using harsh shampoos. Beware of the sudsing shamps. European shamps don't suds as much as ours and are easier on the hair.
Wash as infrequently as possible. The more you wash, the more the scalp revs up its oil production to replace essential oils and maintain microbe balance in the epidermis. Leave in a bit of conditioner so the scalp isn't totally moisture free after the wash, don't rinse it all out. (conditioners should not exacerbate acne, you can use witchhazel once you get out of the shower to make sure your face is oil-free if you wish.)
A famous hot oil concoction is 1/3 olive, 1/3 almond, 1/3 coconut oil simmered thoroughly first and then left on as long as you can, wash out. This is what they do in India. I'm planning on trying it. :) Hot oil treatments on the head are also good for depression, irritability, insomnia.
Really thin hair doesn't need a conditioner so much as what they call an acid rinse to control fly-aways.
Hope that helps! :)