How it happens: Fine, straight hair can become limp when exposed to humidity. "Moisture from the air settles on the surface of this type of hair instead of penetrating it," says stylist Armando Corral. In other words, it weighs hair down.
To fix it now: Add volume at the roots with an antihumidity hair spray. (Try V05 Max! Hold Fast Drying Hair Spray, $3.50 at drugstores.) Divide the top layer of hair into four sections. Lift each section at the roots and spritz the underside. Give the spray a minute to dry, then gently back-comb each section.
To prevent it next time: Lay off the heavy styling products. It's tempting to douse fine hair with volumizing sprays to help combat limpness, but these products cause buildup at the roots and, in humid weather, flatten hair even more.
Bulk up with protein. "Fine, straight hair lacks protein, which gives hair body and helps it hold a style in humidity, says stylist Erica Colameta. To add it, shampoo and condition twice a week with protein-rich products, like Aveda Smooth Infusion shampoo and conditioner ($21 each, aveda.com).
2 of 4Alli Arnold
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, 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.
3 of 4Alli Arnold
Problem: Your Hair Feels Fried and Looks Dull
How it happens: Chlorine and salt water sap moisture from already dry hair and rough up its cuticles, giving it that lackluster look. Overusing products, which is common in heat and humidity, can also cause dullness. "The more product residue, the less light your hair is going to reflect," says stylist Keith Harold. Translation: no shine.
To fix it now: Use a heated iron on your hair (a flat iron if you wear it straight; a curling iron if you like waves or curls). The heat from these tools seals the cuticles, letting hair lie flat and reflect more light. Just don't overdo it. Using these tools more than a couple of times a week can make hair even drier.
To prevent it next time: Use a clarifying shampoo to rinse away product buildup and any residue left by chlorine or salt water. (Try Kenra Clarifying Shampoo, $13, kenra.com for stores.) These formulations are gentle on dry, color-treated, and damaged hair.
Glaze your hair. Both salon and at-home glazes protect all hair types from sun damage and seal in moisture by combining mild dyes with shine enhancers to leave strands smooth and glossy. (Try John Frieda Luminous Color Glaze Clear Shine, $10 at drugstores.)
4 of 4Alli Arnold
Problem: Your Hair Resembles a Steel-Wool Pad: Puffy and Frizzy
How it happens: Curly, coarse, and chemically treated hair is often moisture deprived, so the cuticles on each strand are raised, making the hair more porous. This type of hair absorbs moisture from the air, which makes the hair shafts swell up. The result: big, unwieldy hair.
To fix it now: Fight frizz with a moisture-blocking styling cream or serum, like Arrojo Defrizz Serum ($16, store.arrojoproduct.com). Look for products with silicone or oil to smooth and slightly weigh down hair. Rub a quarter-size dollop between your hands and work it through the strands.
To prevent it next time: Get the right cut. Layers, which add volume, encourage poufiness in the summer. Ask for a blunter cut, which holds down the ends and reduces the fluff factor. Make sure your stylist cuts with scissors, not a razor, which thins out hair, making it prone to frizz.
Keep hair hydrated. Use an oil treatment to seal cuticles so hair can't absorb moisture, says stylist Abell Oujaddou. Apply from roots to ends, leave in for 15 to 20 minutes, then rinse well.