I had AA then AU, for over 20 yrs. I have, like others, always wondered what my trigger the auto-immunity. There are many small indications in the published literature that fungal infection might trigger the process, a candidate fungus being Alternaria [ see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3543859/ ]
There are no clinical trials of anti-fungals, and my hypoethisis would be that it is a superficial infection, rather than a systemic one, and hence could be treated at the surface.
From time to time I have had tiny amounts of vellous re-growth which never lasts. When I had some re-growth about 20 months ago, I started using topical antifungals. I use a small amount of ketoconazole shampoo - about 1cc rubbed onto my head and face, and left in contact for 1-2 mins then rinsed off. I started doing this twice a week, now I do it each night in the bath. I also spray a little terbinafine 2% aqueous spra onto my face, eyebrows, and scapl, and rub it in. Again, was twice a week, now about 4x a week when I remember. The result has been about 60% re-growth of hair on my scalp, about 40% beard re-growth, and about 70% eyebrow re-growth. Lower lid lashes have re-grown, none on uper lids as yet. During the 20 months there have been 2 periods of localised hair loss in my scalp, and these have re-grown. There has been no regrowth of body hair ( I do not treat except my head).
Now, i have absolutely no idea if this is a chance experience. However, hair regrowth in AU is very rare, and none has regrown in my case except in the areas I am treating.
I am posting here not as a snakeoil merchant - we have all seen too many of these - but in case someone else wants to try this method, in case they can repeat my experience. if they can then we are on to something for sure...
Note, there are no published trials of antifungals in AA/AT/AU.
Also note the antifingals I mention are available at high-street chemists without prescription, and will not break the bank. I estimate the cost is about 30p a day.