A Johns Hopkins review of 19 studies has found that many hairstyles can lead to a condition known as traction alopecia. That’s the gradual loss of hairfrom damage to the follicle due to prolonged or repeated tension on the roots. It’s especially common among black women, but can affect anyone.

(HealthDay)—Hairstyles are a defining feature for many people, but some ‘dos can also damage hair follicles.

The researchers categorized common hairdos and styling techniques as low-, moderate- and high-risk, based on the degree to which they expose follicles to factors like tension, weight, heat and chemicals.

Most damaging are hairstyles with a lot of tension or pulling in one direction, like tight ponytails, braids, knots and buns, as well as dreadlocks, weaves and extensions—especially when these are attached to chemically straightened hair. Straightening can also can lead to breakage. Extensions can also cause damage when glued directly onto the scalp and later removed. Tight styles and the added weight of hair enhancements can lead to breakage and eventually loss.

Moderate risk comes from excessive straightening with flat irons and blow dryers, which weakens hair shafts and increases the likelihood of hair loss from additional styling. Also of concern are chemicals used in permanent waves and wigs that are attached with clips and adhesives.

Low-risk hairdos are loose buns and hanging styles that don’t pull on the hair.

To minimize damage, don’t leave in braids longer than two to three months. Remove weaves and extensions after six to eight weeks so follicles can recover from stress. And avoid wearing updos every day; vary your hairstyles regularly.