Many of us obsess about the health of our skin, but how many pay the same attention to the health of our hair? We color, brush, and style it, and we blast it with heat and chemicals. Some hair takes a significant amount of abuse, and the result of all that mistreatment is a mane that’s dull, lifeless, frizzy, and prone to breakage.

But not all bad hair habits are created equal. Many people would confess to the occasional dalliance with the “hot” button on their hair dryer, but how does that compare with the occasional bleach job? Which causes more damage? We’ve ranked the most common hair no-nos, from the slightly sinful to the dangerously damaging.

Temporary Hair Color
Products like Level 1 rinses, washes, stains, and color-depositing shampoos cause virtually no damage to the hair. Since they do not contain chemicals that allow the color molecules to penetrate the hair shaft and interact with the hair’s natural pigments, they merely sit on top of the strands until they wash away, in about six to ten shampoos. Threat Level: Damage-Free!

Hot Showers
In addition to being bad for skin, washing with hot water is a poor choice for hair. It rinses away natural protective oils and accelerates the fading process for colored hair. It’s a myth that a final rinse with cool water will close the hair’s cuticle, but using tepid water in general is much gentler on hair. Threat Level: 1 out of 10 (with 10 being the highest threat level)

Brushing When Wet
When hair is wet, it’s significantly weaker, and brushing it in this vulnerable condition leads to increased breakage. The individual strands can’t handle the tugging and tension, so they stretch until they snap. To detangle wet hair during or after the shower, gently use a wide-toothed comb, working from the ends upward. Better yet: use your fingers. Threat Level: 2 out of 10

Demi-Permanent Color
Non-permanent Level 2 color, a popular at-home option, is generally safe for hair, but it’s not 100 percent gentle. Demi-permanent dyes (like Clairol’s Natural Instincts) contain no ammonia, but they still have a small amount of peroxide to open the hair cuticle and deposit the color molecules. Even though demi-permanent color cannot lighten hair, it still causes a small amount of damage, especially when compounded by other harsh styling practices. Threat Level: 3 out of 10

Perms
The principal chemical used in permanent waves, ammonium thioglycolate, actually loosens the bonds between the molecules of the hair shaft and allows the hair to take whatever shape it’s set in—in the case of perms, on rollers. While any chemical process causes some amount of damage, perms are considered one of the more reliable treatments, as long as the hair is healthy beforehand. Threat Level: 3 out of 10

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Permanent Hair Color
Since permanent hair color involves significant amounts of peroxide and ammonia, it can cause significant amounts of damage, including dryness, breakage, and dullness. The most potentially damaging color transition is in lightening dark hair, which requires two separate processes, the removal of the original color and the depositing of the new color. After this much chemical meddling, hair is in a significantly weaker state than it was when it started. All bottle blonds should take care to condition their hair regularly and treat it gently. Threat Level: 4 out of 10

Blow-Drying/Flat-Ironing
The occasional blast from a hair dryer won’t harm hair too much, but the heat from daily use of a blow dryer or flatiron causes hair to become extremely dry and brittle. Hair in this weakened condition is more susceptible to damage from other stressors, leading it to lose elasticity and break. For daily dryers, stylists recommend allowing hair to partially air-dry before blow-drying, or blow-drying it until it’s only about 80 percent dry and then allowing it to air-dry the rest of the way. Threat Level: 4 out of 10

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