Shea Moisture has become a go-to brand for those ... Biolage Advanced Full Density Thickening Shampoo Biolage takes a scientific approach to fighting thinning hair. Byrdie loves its dual-action ...

There's also shea butter to deeply moisturize and avocado oil, which forms a protective layer around each strand to reduce breakage. “Hair-thickening shampoos typically act in two possible ways ...