Any shampoo's which genuinely make hair thicker?

Every hair shampoo on the market promises that it promotes thicker, healthier looking hair. Are there any that have actually been clinically proven to do so? Or is it all just so much marketing bullshit?

When I had an extremely low vitamin and iron level I was losing my hair. My hairdresser suggested using Nioxin - I researched and decided to give it a try. It was like 3x as expensive several years ago as it is now, but very effective. I still use it today because my hair is naturally thin.

When my son decided to (be a dumb ass and) shave his head just before senior pictures, I gave him a set - shampoo and a scalp treatment- and his hair grew back fast and thicker.

What would be the definition of “promotes thicker, healthier looking hair”? That sounds like it means if you have thick healthy looking hair, our shampoo will “promote” it. Whatever that means.

You can get volumizing products which lift the hair up from the root and make it appear fuller than it is. As for actual thickening, I am not sure.

Nitpick: “Any shampoos…”

Apostrophes do NOT mean, “Here comes an ‘s’!”

no cite,
but as I understand it, “hair thickening” shampoos are equipped with a wax that coats the individual hairs making them seem thicker. That seems to qualify the OP: “thicker healthier looking hair”. Since hair is dead, not sure what healthier hair really is. Dead is pretty unhealthy as far as I know.

While we’re on the topic of shampoos and advertising claims, what exactly do they mean when they say “hair is (up to) 5 times stronger”

Do they string up a weight to a piece of hair and keep going til it breaks? Are we to believe after using the shampoo that it would take 5 times the weight to break the hair?