Summer: the magical season when hair appears to triple in size within a day. “Hair expands and gets frizzy because it lacks moisture,” says hairstylist Sarah Amson, co-owner of Bang Salon in Toronto. “A lot of people shy away from hydrating products because they think they’re going to weigh their hair down, but there’s moisture for every hair type.” If you have fine hair, use a leave-in spray; those with medium and coarser textures can opt for a cream. Try: Kevin.Murphy Staying. Alive ($28), Garnier Whole Blends Avocado Oil & Shea Butter Nourishing Rinse Out Mask ($9) or Bumble and Bumble Bb.Curl Custom Conditioner ($42).