Problem: Your hair looks soppy and greasy.

How It Happens: It’s hot. Your scalp sweats. And its sebum, or natural oils, ride that wave, spreading throughout the hair and making it look a little too grunge for this decade. Even worse, “most styling products are water soluble, so your sweat can break them down until they no longer work,” says stylist Keith Harold. That means your style falls flat, too.

To Fix It Now: Sprinkle a hair powder on the scalp to help absorb excess sebum. (Try Hair Fix, $20, www.myhairfix.com.) Apply a small amount to the roots, leave it in for one minute, then comb through or shake hair gently to remove any excess. If powder makes your hair look dull, finish with a shot of hair spray, which adds shine without any oil.

To Prevent It Next Time: Wash your hair less often. Sounds counterintuitive, but “daily washing causes your scalp to overproduce oil to replace the natural oil you’re washing away,” says stylist Sarah Potempa.

When you do wash, don’t overdo it. Avoid scrubbing the scalp vigorously, which causes it to produce more oil. Instead, allow shampoo to sit on the hair and scalp for one minute before rinsing. Apply conditioner to the ends only.