The cold setting on a blow dryer turns off the heating element and blows room-temperature air through the barrel using only the fan motor. This isn’t just a gentler way to dry your hair. It serves a specific purpose in styling: cool air locks your hair into whatever shape you’ve created with heat, making the style last longer and leaving the surface smoother and shinier.
What Happens Inside the Dryer
A blow dryer on its hot setting draws between 1,200 and 1,875 watts of power, with most of that energy going to the heating element. When you switch to the cold setting, the heating element shuts off entirely. The motor and fan keep running, but power consumption drops to roughly 70 to 140 watts. Some models use as little as 66 watts in unheated mode. You’re essentially running a small, focused fan at that point.
Most blow dryers offer the cold function in one of two ways: a dedicated “cool shot” button you hold down temporarily, or a separate cool setting on the temperature dial that you can leave on continuously. The cool shot button is designed for quick blasts of cold air between sections of styling, while the dial setting works for longer, gentler drying.
How Cool Air Locks In a Style
The real value of the cold setting comes down to what’s happening at the molecular level inside each strand of hair. Your hair is made of proteins held together by weak connections called hydrogen bonds. These bonds are what give your hair its natural shape, whether that’s straight, wavy, or curly.
When you apply heat, those hydrogen bonds weaken and break apart temporarily. This is why hot air makes hair pliable and easy to reshape. You can wrap it around a round brush, pull it straight, or coil it into a curl, and the softened protein structure goes along with it. But while the hair is still warm, it hasn’t committed to that new shape. The bonds are still loose, and the style can fall apart quickly.
Cool air reverses that process. As the temperature drops, hydrogen bonds re-form between the proteins, but now they lock into the new configuration you’ve created. The style holds until those proteins gradually return to their natural structure, which happens over time through movement, humidity, and the next time you wash your hair. This is why a blast of cold air after curling a section with a round brush makes the curl bouncier and longer-lasting than heat alone.
Why Cold Air Reduces Frizz and Adds Shine
Each strand of hair is covered in a layer of tiny overlapping scales called the cuticle. Think of it like roof shingles. When this layer lies flat, light bounces off it evenly, and your hair looks smooth and shiny. When the scales lift up, the surface becomes rough, light scatters in all directions, and your hair looks dull and frizzy.
Heat opens the cuticle. That’s useful during styling because it allows products to penetrate and makes the hair more flexible. But if you stop there and let your hair cool on its own or walk into humid air with the cuticle still lifted, moisture from the environment sneaks in, swells the strand, and creates frizz. Cold air contracts the cuticle and seals those scales back down, creating a smoother surface that resists humidity. The result is hair that holds its texture throughout the day and reflects more light, giving it visible shine without needing a flat iron.
Does Cool Air Protect Hair From Damage?
The relationship between dryer temperature and hair damage is more nuanced than you might expect. A study published in the Annals of Dermatology tested hair dried at different temperatures and found that the internal structure of the hair, including the cortex and melanin granules, showed no damage at any temperature tested. The hair’s outer cuticle layer acted as a barrier protecting the interior. Even moisture content after drying didn’t differ significantly between temperature groups, suggesting that how you dry your hair matters less for hydration than people often assume.
That said, the study measured the effects of controlled drying sessions, not the cumulative wear of daily high-heat use over months or years. Where cool air clearly helps is at the surface level. Repeatedly blasting open cuticles with heat and never sealing them back down leads to rougher, more porous hair over time. Using the cold setting to close the cuticle after each heat styling session reduces that surface-level wear, keeping hair looking healthier between cuts.
How to Use the Cold Setting Effectively
The cold setting works best as a finishing step, not a replacement for hot air. Start by rough-drying your hair with warm or hot air until it’s about 80% dry. Then style each section with heat and a brush, shaping it into the position you want. Once a section is in place, hold down the cool shot button while keeping the hair in its styled position for several seconds. This is the moment the hydrogen bonds reset. Release the hair and move on to the next section.
For a full blowout, the process is section by section: heat to shape, cool to set. If you’re going for volume, lift a section at the root with your brush, hit it with warm air, then blast it with cool air before releasing. For smoothing, wrap the section taut around the brush, dry with heat, then switch to cool while slowly pulling the brush through to the ends.
You can also use the cool setting for a final all-over pass once your style is complete. A 30-second sweep of cold air over your entire head helps seal the cuticle across every section and gives the style a polished finish. This last step is especially useful in humid climates, where frizz can undo your work within minutes of stepping outside.