NOTE - I tried creating a new post but it's not been approved for weeks so I want to get this out there and I can change this if necessary if my post gets approved.
I did a search and didn't find much regarding using topical garlic. So here is my experience.
Earlier this year a sincerely tried fresh garlic slices on my bald spots (right forearm and eyebrows, though I have plenty more spots that act as controls).
As my forearm bald spot is quite a large area, I actually tried garlic, ginger, and onions beside each other. Fortunately I didn't have to go out much. ;-)
The only area that started to grow was the garlic area, the first good evidence for me.
The other evidence was that other bald spots over my body did not change, if anything they were still getting worse.
How I do it, is cut thin slices of garlic and lay it on the bald spot, then cover it somehow (plastic wrap worked okay for my forearm). Eyebrow was more difficult and for that I would rub the cut garlic on my eyebrow then slice a bit of to get more fresh juice and repeat until it was stinging quite a bit. I would do this once per day.
DURATION BEFORE RESULTS
It took me 2-3 months before really accepting that results were happening. After the first month or two, there was a little bit of growth, but not obvious if it was the garlic or just natural regrowth. After 3-4 months It was really obvious to me, normal hairs not fine white hairs.
I actually started in beginning March, but on and off. I got serious in April 2021 to until June or July. Then I stopped. Now I'll start up again (and pick some other spots too).
CAUSES OF FAILURE
Here is why I think most times using garlic fails, because it is really tedious, time consuming, stinky, etc! I've stopped lately even though I believe it really works! With a busy life and not being too bothered by bald spots, it's hard to do this every day with fresh garlic. A tip is to peal a bunch of garlic and have it ready in the fridge so that Mon-Fri it's easier to start.
And fortunately the new hairs haven't all fallen out after a month or more of stopping. (tho some have started to, so I better get back to it)
Of course another reason it could fail is that your body just doesn't respond to it. Onion juice didn't seem to work as well as garlic for me, but there are reports of onion juice working for others.
Garlic burns! If you try it, make sure you start with short durations, like 10 minutes a day for several days, monitoring that the skin doesn't get too irritated. The irritation is CUMULATIVE! Once my skin was just a little red and I thought, no big deal so did more the next day and I started getting small blisters. So take it slow, remember it is a several month long process anyway. If it gets too irritated, give it a break for a couple days.
You'll want to get just enough irritation without harming the skin. My understanding is that the irritation is what affects the immune response in the skin. My dermatologist mentioned poison ivy has been reported to work, but that's extreme! Same with some clinical topical treatments she suggested, I forget the name, but the one suggested I read that medication causes tumors in rats, so I'll stick to garlic...
Some may suggest that it could be the normal AA hair cycle, however areas nearby that had no garlic, didn't regrow. Honestly the hardest part is sticking to it daily for months, I don't think the majority of people can do that in reality, which is why I think there's not much good evidence for it (though I did find some official clinical studies that support it).
Take care everyone!