Billy Jealousy Hair Raiser
I really don't believe that it will cause hair to grow, having looked through the ingredients. Nevertheless, its got some good things in it and will probably help a scalp that is being increasingly exposed to the elements look and feel better. It includes squalane, which I don't believe does much for hair loss, but it should buff up the pate nicely. Then there are some plant extracts, including liquorice and, intriguingly, methyl nicotate, which is an inflammatory agent. I think that there is a belief that stimulation of blood vessels stimulates hair growth.
As always, Billy assumes (probably correctly) that his average customer isn't super sensitive and there are one or two ingredients (phenoxyethanol and stearamidoethyl diethylamine) that are known irritants.