Anecdotal evidence suggests that hair dye may kill lice due to the chemical substances it contains, such as ammonia and hydrogen peroxide. However, it is unlikely to kill nits, which hatch as lice.

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Head lice are parasitic insects that live in human hair. They are about the size of a sesame seed and translucent white or brown in color.

Lice feed on human blood and can live for up to 30 days on the scalp, where they lay up to eight eggs, or nits, daily.

Lice are common among young school children, with an estimated 6–12 million lice infestations occurring in the United States in people aged 3–11 years.

This article looks at how hair dye affects lice, how to use hair dye to kill lice, and the safety and precautions of using hair dye. We also discuss alternative lice treatments.

According to anecdotal evidence, permanent hair dye that contains alkaline ammonia is the type that may kill lice.

Ammonia is a common toxic and corrosive substance that produces an irritating gas and has a distinctive smell. Lice may be sensitive to ammonia, which may explain how the chemical and the gas it produces kill the insects.

Permanent hair dye and bleaching solutions also may contain hydrogen peroxide. Studies have found that this chemical effectively treats sea lice, but more research is necessary to determine its effects on head lice.

If unhatched nits remain on the scalp, they will hatch within 9–10 days of being laid, and the lice will return. A person will have to repeat the process if this occurs as hair dye cannot penetrate the egg casing of nits.

The following steps explain how a person can attempt to use hair dye to eliminate head lice:

  • Remove as many lice and nits as possible with a lice comb. Clean the comb thoroughly by soaking it in very hot water between uses.
  • Follow instructions to mix the dye in a well-ventilated area, as ammonia can be unpleasant and harmful to breathe.
  • Apply the dye — saturate the scalp, base of the neck, behind the ears, and coat the base of every hair.
  • Leaving the dye on for the recommended time, then rinse out as instructed.
  • Comb through the hair with the lice comb again.
  • Dry hair at a high heat, which may help kill remaining lice.

If a person unintentionally swallows the dye, it can cause irritation or injury to the mouth and stomach as well as life threatening allergic reactions. Eye exposure may also cause problems such as mild irritation to vision loss.

When dyeing hair, a person should take safety precautions, such as:

  • using disposable gloves, which often come with the dye product
  • avoiding touching the eyes and mouth when handling hair dye
  • not dyeing eyebrows or eyelashes with hair dye

Experts do not recommend using hair dye or bleach on children’s hair to treat lice. Hair dye can damage adult hair and is even more likely to damage children’s hair, which is typically finer and more delicate. Children may also be at higher risk of chemical reactions to the eyes, airways, scalp, and hair.

Permanent hair dye can irritate the scalp and cause side effects, including:

  • swelling
  • redness
  • burning
  • itching
  • hair damage and breakage
  • hives
  • dry hair
  • thinning hair

If a person accidentally swallows hair dye, breathes it in, or gets it in their eyes, they may experience a serious reaction. These include:

A person should seek medical attention immediately if this occurs.

A person can comb their hair using a lice comb, but this is not effective at ridding a person of lice if it is the only treatment. Treatments for lice include:

  • Insecticide-based treatments: Over time, lice have built up their tolerance to many insecticides, so these treatments are not as effective as they once were.
  • Silicone-based treatments: These treatments suffocate lice by covering them in a layer of oil. They do not contain insecticides or pesticides, so do not run the risk of resistance.
  • Plant-based treatments: Treatments such as coconut oil and other home remedies may help eliminate lice, but more research is needed.

Some evidence also suggests vinegar or oil in combination with some hair dye chemicals may help kill or loosen lice. However, these methods are no longer in use due to major adverse effects.

A person must physically remove the lice and nits using a lice comb, even after treatment.

People can buy most lice treatments over the counter. They will usually need to reapply the treatment every 7–10 days until all the lice and nits are gone.

Read on for other home remedies for killing lice.

A person can usually rid themselves of lice with proper treatment. However, the infestation will return if nits or live lice remain in the hair or on the scalp after treatment.

They are highly contagious, so anyone who comes into close contact with a person with lice risks infection.

Hair dye may kill lice as it contains chemicals such as ammonia and hydrogen peroxide, which lice may be sensitive to. However, it is not likely that hair dye can kill nits, which will return as lice once hatched. The effectiveness of hair dye as a lice treatment is anecdotal, and research is needed to determine whether it is an effective option.

A person should take safety precautions, such as wearing gloves and dyeing their hair in a well-ventilated area. This is because the dye can have side effects and cause serious complications if swallowed, inhaled, or transferred into the eyes.

Other treatments for lice include silicone-based treatments and insecticide-based treatments. A person will need to comb out their hair using a lice comb and treat their scalp and hair to rid themselves of lice.