You hop out of the shower in the morning and are running a bit behind, so you blast your hair with the blow dryer instead of letting it air dry. After you’re dressed, you run a flat iron over your strands to smooth out the frizziness that seems to be getting worse. This is your standard morning routine—heat, followed by heat…followed by more heat.

You’ve probably heard that heat styling is bad for your hair, but your hair seems to be fine, so a quick blow dry or heat styling session in the mornings can’t hurt, right? Wrong!

Heat is not inherently bad for the hair. In general, healthy strands can withstand temperatures up to 450 degrees F (232 degrees C) when they’re applied occasionally. Unfortunately, heat that exceeds this temperature, as well as persistent heat application, can lead to damage. Here’s how.

Hair science 101

Each strand of your hair has three layers. An outer layer, called the cuticle, is made of overlapping cells that resemble shingles. These cells are supposed to lay flat but remain flexible, giving shine to the hair and protecting the inner layers from damage. If the cuticle is raised, hair will begin to look frizzy.

The middle layer, called the cortex, is the thickest layer. The cortex contains melanin, the pigment that gives your hair its color, and keratin proteins, which give your hair its shape. These proteins form chemical chains or bonds that help retain moisture and provide strength to the hair. Two of these bonds are disulfide bonds and hydrogen bonds.

• Disulfide bonds must be broken or formed using chemicals. When this happens, you can permanently alter the structure of your hair. Examples include using relaxers to turn curly hair into straight hair or perms to make straight hair curly.
• Hydrogen bonds are much easier to break, being broken and replaced by using water or heat. This temporarily alters the shape of the hair. Examples include how wet hair appears straight until it dries and how you can curl straight hair using a curling wand.

The innermost layer is the medulla. This section provides extra strength for the hair, but it is not always present—especially not in light-colored hair.

How heat styling alters hair

When you heat style your hair, you alter the hydrogen bonds in your hair, breaking these bonds down and temporarily changing your hair’s shape. Heat styling does not affect the disulfide bonds in your hair, which is why your locks return to their natural shape after a few hours.

Unfortunately, heat can do much more than temporarily change protein bonds. Blow drying your hair with high heat can lead to the rapid evaporation of moisture, drying it out. This is most likely to affect the cuticle, but can also penetrate deeper, into the cortex. Water is crucial in maintaining your hair’s structure, strength and elasticity. Without enough moisture, your strands will look lifeless, brittle and frizzy.

Additionally, excessive heat from flat irons or curling wands can damage the cuticle, reducing the protection this layer offers the rest of your hair. Once the cuticle is cracked, bubbled or totally lost, future moisture loss and damage can occur—with or without heat application!

Can you repair heat damage?

Unfortunately, you can’t repair heat-damaged hair. Products and styling tips can help mask the appearance of damaged hair, potentially making it look healthier than it is, but hair scorched by heat will never recover. It’s best to cut off damaged hair and let it grow out healthy once again.

However, you can take steps to prevent heat damage:

• Use heat protectant: Heat protectant products coat the hair with water-soluble silicones. These protect the outermost layers of your hair from heat damage while helping your strands retain their moisture. Silicone products can build up over time, and you may need to use a clarifying shampoo to rinse them out every month, but they can do a lot to protect your hair from damage if you have to style with heat.
• Lower the temperature: Your hot tools don’t need to be as hot as you think they do! Most people damage their hair by setting their curling wands and flat irons far too high. Start with the lowest setting and slowly increase as necessary. If you have fine hair, you’ll want to stick to the lowest setting possible, since your hair will be more prone to damage.
• Limit heat styling: Try to avoid heat styling as much as you can, limiting it to once or twice per week. There are many other ways to style your hair without heat. If it’s possible for you to avoid heat styling entirely, you’ll be able to protect your strands that much more!
• Keep hair healthy and strong: Healthy hair will stand up to heat much more effectively than hair that is already dry, damaged or brittle. Take care to nourish your hair inside and out by eating healthy foods, drinking lots of water, taking hair care supplements, using the right shampoo and conditioner for your hair type and applying hair masks to help it retain moisture.

Heat styling doesn’t have to result in damage for your hair—you just need to be smart about it! By staying mindful about how heat alters your hair and what its potential effects are, you can reduce your risk for heat-scorched locks and retain shine, bounce and beautiful hair!