Rosemary got its reputation from people massaging the oil into their scalps on camera and swearing it helped, on the theory that it boosts circulation. The shampoo aisle caught up fast. The catch is that a shampoo sits on your head for about a minute before it goes down the drain, which is a very different thing from an oil left on for hours. So I sorted these by what each formula does, and put a few thickening washes next to the rosemary ones for anyone whose real worry is thinning. Nécessaire makes the quiet grown-up version, BondiBoost goes straight at thinning, and Davines' energizing shampoo is a salon brand's take on the same concern.

This group is for hair that looks thinner than it used to. Dr. Groot and Virtue both make thickening shampoos for exactly that, washes that work on how full your hair looks day to day while the slower work happens elsewhere. Nécessaire's conditioner carries the rosemary through the lengths. The BondiBoost drops are a leave-on serum, the format closest to the overnight oil routine that started this whole thing.

When dry shampoo and styling product have piled up for a few days, Briogeo's charcoal and coconut oil scrub shampoo is the one to grab, since it exfoliates while it cleans. Dr.FORHAIR is the Korean scalp care brand developed with trichologists, and its Folligen thickening shampoo counts rosemary among its ingredients, which makes it the easy everyday wash in this group. The pre-wash products are where I would actually focus. Briogeo's rosemary scalp oil and the BondiBoost lactic acid treatment go on before shampoo and sit for a while, which gives the ingredients far more time on the scalp than any rinse-off wash can.

Nécessaire's rosemary serum is the one I would reach for if thinning is the real worry, because it stays on the scalp instead of rinsing off. Philip Kingsley, the London trichology clinic that has been treating hair and scalps since the 1960s, makes a thickening shampoo for thinning hair to use alongside it. The salt scrubs from RŌZ and Goop Beauty loosen flakes and buildup before you wash. Keep the scrubs to once a week or so. A scalp that gets scrubbed every day usually lets you know it is not happy.

Rosemary shampoo is a genuinely nice wash. It smells clean, it feels good on the scalp, and nothing here is one I would warn you away from. What it gets oversold on is regrowth, because a rinse-off formula does not stay on the scalp long enough to do what a leave-on oil might. If you take one thing away, choose these for how they wash and feel, and if thinning is the real worry, lean on the leave-on and pre-wash formats or ask a dermatologist about a treatment with clinical testing behind it. If you want to keep browsing, I also put together Briogeo Began in a Family Kitchen and Briogeo Shampoo, From Four Products and a Goldman Sachs Desk.