> https://www.mdpi.com/2076-3921/13/12/1549
The human equivalent dose of luteolin would be about 3g/day, which is a lot -- but this makes it more interesting, for although luteolin has been available as a nutritional supplement for decades, I don't think that people have normally taken it at that sort of dose. Or anywhere near that sort of dose.
Luteolin is a weak yellow dye, but there are presumably ways to formulate it for topical use so that it's colorless. In general, it's usually pretty easy to get chemicals into follicles. (As opposed to through the skin, e.g. with a nicotine patch, which is possible but more difficult.) If this stuff works, it'll be a staple of haircare and anti-aging products for decades.
It's not in that particular study, but more potent analogs appear to exist. They lack luteolin's easy off-the-shelf availability, though, and presumably the mechanism of action is the same at any rate.