Healthy hair starts with a healthy scalp. It’s a fact we’ve become increasingly aware of over the years, and brands are responding with solutions — lots of them. What was once a niche category, growth-promoting scalp serums have exploded in number. So when a specific scalp serum sells out (numerous times), and boasts thousands of five-star ratings and a flurry of shopper praise, it stands out from the rest. 

Such is the case for the Stem Cell Scalp Serum from Act + Acre, a tiny yet mighty bottle of scalp-nourishing, growth-promoting goodness. The highly lauded serum — which has amassed waitlists of over 18,000 people — is already sold out in its standard size, but its mini version is available and on sale exclusively for InStyle readers during our InSider Sale, where you can score major discounts on 12 of our favorite fashion and beauty brands for just a few more hours.

For a limited time, you can shop Act + Acre’s now-$34 mini serum, in addition to any other product on the brand’s site, for 25 percent off with code INSTYLE25. Hurry — you have until 11:59 p.m. ET tonight to snag this limited-time deal.

Act+ Acre

The Act + Acre Mini Stem Cell Scalp Serum is a science-backed solution for hair shedding and stunted growth. According to the brand, the serum “extends the growth phase,” i.e. the anagen phase, of the natural hair-growth cycle to promote longer, fuller hair. Furthermore, it strengthens strands, which translates to less breakage and shedding over time. The formula is drug- and fragrance-free, and stylishly packaged in a minimalistic bottle. Application is similarly simple, and requires no rinsing, making it a breeze to incorporate it into any routine. 

Swiss apple stem cells star as the serum’s main growth-supporting ingredient. Protein-rich pea extract densifies and strengthens weak, brittle strands, and aloe vera adds soothing hydration to the scalp. 

Though the serum may be the brand’s buzziest and best-selling product, don’t sleep on Act + Acre’s satisfying scalp exfoliators which remove buildup, stylish shampoo sets that promote thicker-looking hair, and more — all of which are also 25 percent off for InStyle readers through tomorrow with code INSTYLE25.

Act + Acre

Shop the hair growth serum thousands of shoppers have eagerly snapped up, plus more hair-loving product wins from Act + Acre and other brands during the InStyle InSider Sale — and hurry. Deals end soon.