Hair serums are treatment and/or styling products that smooth frizz, add shine, fortify strands and help protect hair from heat and UV damage. They are applied to specific areas of the hair, focusing on mid-lengths to ends. 

In contrast, scalp serums are designed to help improve scalp health, targeting issues like collagen loss, dryness, hair density, thinning and shedding.

For example, Color Wow's Youth Juice Scalp Serum helps protect and support optimal scalp collagen to promote thicker, stronger, healthier-looking hair strands​.

Hair serums are applied to damp or dry hair, usually concentrating on the mid-lengths and ends. Scalp serums are applied directly to the scalp along the hairline and parting. They are massaged into the scalp to promote an optimal  environment for hair growth.

Typically, hair serums are not meant for the scalp since they focus on addressing issues with the hair strands, like adding shine or reducing frizz. Applying hair serum to the scalp could make it look oily and even cause irritation. 

Scalp serums, however, are formulated for direct application to the scalp to help address issues like thinning, weaker, sparser strands and shedding.