Hair dyes are chemicals that people can use to change the color of their hair. The agents in dyes can weaken and damage hair, which may make it look unhealthy. However, treatments such as conditioners and specially formulated shampoos may help repair hair damage from hair dye.

Dyeing the hair with chemical or natural dyes can damage hair. This is because the dye may affect proteins and lipids present in the hair, which contribute to hair health. Changes to the inner and outer structure of the hair shaft can damage hair, making it fragile and prone to breakage, which could eventually result in thinning hair or hair loss in areas.

Hair dyes can weaken hair, but people can take precautions to minimize potential damage if they still choose to dye their hair. Additionally, other tips are available to help replenish hair and keep it healthy.

In this article, we look at the effects of hair dye on hair health and tips to repair hair damage and maintain healthy hair.

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Hair consists of an inner cortex, which contains most of the hair mass, and keratin proteins. An outer layer of hair called the cuticle encases and protects the cortex. Hair lipids play an important part in healthy hair and contribute to around 2–6% of the weight of hair. Hair lipids affect the shine and feel of the hair, as well as hair strength.

Hair dye is a topical substance that changes the color of hair either temporarily, semi-permanently, or permanently. While dyeing hair is a common practice, it can damage the hair shaft, making it fragile and more prone to breakage.

Most permanent hair dyes use a combination of ammonia, hydrogen peroxide, and p-phenylenediamine (PPD) to color the hair. Ammonia opens up protein layers in the hair, which allows the dye to coat the hair shaft. Hydrogen peroxide strips hair of its natural color, and PPD then bonds into the hair to color it.

Dyeing the hair in any way can cause damage to the hair through:

  • changing the structure of the cuticle layer of the hair
  • breaking down protein in hair
  • loss of hair lipids

According to a 2020 article, PPD is an allergen that can cause allergic contact dermatitis. Along with skin irritation, PPD may also have a link to health problems such as congenital abnormalities (formerly known as birth defects) and liver and blood toxicity.

A 2018 study found that bleaching hair with peroxide resulted in oxidative damage and protein loss in the cuticle and cortex of the hair.

Products labeled as “natural” or “organic” may also produce negative effects. Natural sources, such as plants, can still contain harmful or allergenic substances.

The Food and Drug Administration (FDA) states that because a product is organic or contains organic ingredients, it does not mean that it is automatically safer.

Additionally, growing evidence suggests that some hair dyes may contain endocrine-disrupting compounds. These chemicals can mimic the effects of the hormone estrogen and may increase the risk of breast cancer. Namely, research suggests that permanent dyes may contain higher concentrations of aromatic amines, which may be carcinogenic to humans.

Other potentially harmful ingredients may include ammonia and toluene. The former is a respiratory irritant that can trigger asthma attacks, and toluene is a known neurotoxin with links to congenital abnormalities, pregnancy loss, and allergic reactions.

While these are common ingredients, hair dye options exist that do not use harsh chemicals. People may wish to look at labels or ingredient lists on products to check for chemicals that may be harmful.

The type of hair dye may affect how much hair damage occurs. Hair damage can occur in any hair type, as it affects the inner and outer structure and makeup of the hair.

Temporary dyes only reach the outer layers of the hair shaft and often wash away with one shampoo wash.

Semi-permanent dyes remove natural coloring from the hair shaft but are weaker than permanent dyes. This means they tend to cause less damage. Semi-permanent dyes typically wash out within 4–12 shampoo washes.

Permanent dyes penetrate deeper into the cortex of the hair, bleach the natural coloring, and trap color particles within the hair shaft. This process can damage the hair.

The difference between natural hair color and the color people want to dye their hair may also play a part in hair damage. The bigger the difference between natural color and dye color, the more damage may occur. A 2018 study found that protein loss increased based on how severe the bleaching was with peroxide hair dye.

Natural dyes can also damage hair. According to a 2019 study that used goat hair in place of human hair, henna dye damaged the hair cuticle.

Hair dye will affect hair strands until the color grows out. To minimize the damage from hair dye, people can choose a conditioning hair dye. According to a 2018 study, hair dyes containing conditioning agents such as hydrolyzed silk or milk protein may reduce the damage from dyeing hair.

Using shampoos that include lipids, such as fatty alcohols, can also help to replenish lipids in the hair and improve hair strength.

The American Academy of Dermatology Association recommends the following hair care tips for dyeing the hair and maintaining general hair health:

  • Use a specially formulated shampoo for color-treated hair.
  • Stay as close to the natural hair shade as possible, staying within three shades of the natural color and darkening rather than lightening where possible.
  • Protect the hair from the sun by wearing a hat in sunny weather.
  • If perming the hair, follow product instructions carefully to avoid any long-term damage.
  • If using a relaxer, consult a professional to ensure safe application.
  • If having multiple treatments, such as coloring, perming, or relaxing, try to space out the time between services.
  • Use conditioner after every hair wash, especially on the ends of the hair.
  • Minimize heat on the hair, such as from styling tongs, and apply a heat-protective product beforehand.
  • Choose hair products that match hair type.
  • Protect hair from chlorinated water by wearing a tight-fitting cap when swimming.
  • Carry out a patch test of hair dye before applying it all over to check for any irritation.

To check for an allergic reaction to a hair dye, people can first perform a patch test. Each hair dye product may have individual instructions for a patch test that people can follow.

A patch test typically involves applying a small amount of hair dye behind the ear or on the inner elbow, covering an area of about 1 square centimeter. People can then leave the dye to dry and monitor the area for any signs of irritation. It may help to wait a few days after this test, as a reaction may not happen immediately. If there are no signs of irritation, people can then apply the dye to the area of hair they want to color.

Certain ingredients in hair dye, such as PPD, may cause an allergic reaction. The following can be signs of an allergic reaction:

  • irritation
  • swelling
  • itching
  • sores
  • a burning sensation
  • skin discoloration

An allergic reaction may occur straight after using a product or a few days later. If people have any swelling of the face or neck or any difficulty breathing, it could be a sign of a severe allergic reaction, and they must seek immediate medical help.

All types of hair dye change the appearance of hair. Some, particularly permanent hair dyes, alter the structure and makeup of the hair. Many hair dyes can damage both the inner and outer parts of the hair shaft. Both natural and synthetic dyes may weaken hair, but permanent dyes may cause more damage as they penetrate deeper into the hair shaft.

To minimize damage from hair dye or help replenish hair, people can choose hair dyes that contain conditioners. Additionally, using shampoos containing lipids and proteins may help repair damage. People can follow general hair care tips, such as avoiding heat, tension, and other chemicals to maintain hair health.