Hair dye products are becoming increasingly popular, but is semi-permanent hair dye damaging to your hair? Research from the United States found that 33% of women used semi-permanent hair dye in 2021, making it the most popular type of hair dye [1].
This hair colouring product can add a pop of colour to your hair and give you a confidence boost, but you may wonder whether the results are worth it. Here’s everything you need to know about semi-permanent hair dye, including:
It’s easy to get confused with all the different types of hair dye, which can be classed as permanent, semi-permanent, demi-permanent, gradual, or temporary.
Semi-permanent hair dye does not contain ammonia, which is often found in permanent hair dyes. This is a chemical that lifts the outer part of the hair shaft so hair dye can be deposited on the inner cortex, making it permanent. The colour from semi-permanent dye doesn’t reach your hair’s cortex, therefore the colour doesn’t last very long.
Pigments in semi-permanent dye gather around the outer part of your hair shaft, rather than entering the inner cortex. This means that they only remain for several washes, gradually fading each time. Semi-permanent dye usually lasts between 4-12 shampoos before you need to re-dye your hair.
Semi-permanent hair dye does not last as long as demi-permanent (which lasts up to 24 washes), and it does not need to be mixed with a developer (oxidant) [2]. Hair developer contains hydrogen peroxide, which bleaches the hair and helps the dye become trapped in the hair, which can be damaging if overused. The ingredients in semi-permanent dyes still contain some hydrogen peroxide, but much less than is used in permanent dyes [2].
Semi-permanent hair dye is less damaging to your hair than permanent dye because it doesn’t penetrate as deep into the hair shaft [2]. It is designed to mainly coat the outer shaft of your hair, meaning much of the inner hair cortex is protected from damage.
The molecules of semi-permanent hair dyes are capable of penetrating the cortex [2]. However, they don’t join together once inside the cortex and become even larger (like the molecules of permanent dyes do), so they are easily removed by shampooing [2].
Polymerization (enlargement) of hair dye molecules requires an oxidising agent, and the differences in the level of this agent regulate the degree of polymerization. Molecules that become trapped change the colour of the hair shaft forever – that’s how permanent dyes work. In addition, permanent dyes chemically react with the hair proteins, which anchors them in the cortex permanently.
Because semi-permanent hair dye doesn’t penetrate your hair as deeply as permanent dye, it is not able to alter your hair’s natural texture or melanin (the natural pigment in your hair). However, semi-permanent dye still causes some degree of damage and can cause dry, brittle hair.
The hydrogen peroxide found in semi-permanent dyes can stop your hair follicles and pores on your scalp from producing sebum. These natural oils include lipids and proteins which are vital for smooth, healthy hair.
Therefore, long-term use of semi-permanent hair dyes can cause hair breakage, dryness and tangling. Higher concentrations of hydrogen peroxide have been found to cause greater hair damage [3]. Essential oils for hair growth can be used for dry hair caused by hydrogen peroxide.
Semi-permanent hair dye can be particularly harmful if you have colour-treated, fragile, or damaged hair to begin with. These hair strands tend to be more porous, making them more vulnerable to further damage.
If your hair is more porous than it should be, semi-permanent dye may penetrate deeper into the hair shaft than usual. This can cause it to act more like permanent hair dye, with longer-lasting results but greater hair damage.
Overall, the risk to your health from toxins in semi-permanent hair dye is low [4]. However, it depends on which dye or colour you choose. For example, Basic Red 51, a permitted semi-permanent hair dye, has been found to be cytotoxic to human skin cells [5]. This means that it harms cells it comes into contact with (such as those on the scalp), which can increase your risk of some types of cancer.
Your risk from semi-permanent hair dye may also depend on where you live. There are two chemicals found in some semi-permanent hair dyes (2-nitro-p-phenylenediamine and 4-nitro-o-phenylenediamine) that are known to increase your risk of cancer [4]. These two chemicals are banned in Europe and the United States following testing that proved this risk [4], but may still be available in other countries.
Many hair dyes, both permanent and semi-permanent, contain ingredients that can cause an allergic reaction or irritate your skin [6]. Darker hair dyes tend to pose a stronger risk of allergic reaction than lighter-coloured on [6].
Some people may experience symptoms of contact dermatitis when they use semi-permanent hair dye [6]. The dye can cause skin to become scaly, dry, blistered, lumpy, or inflamed where it touches your skin.
Some semi-permanent dyes contain a chemical called paraphenylenediamine (PPD), which causes most allergic reactions to hair dye [6]. There is more PPD in darker shades of hair dye.
Serious reactions to hair dye are possible, especially to those that contain higher levels of PPD. You are more at risk of a reaction if you have ever had a black henna tattoo because the henna paste often contains large amounts of PPD, which can increase your risk of a life-threatening reaction the next time you are exposed to it [6].
Symptoms of an allergic reaction to PPD range from mild to severe. Mild irritation may show as burning, stinging, or inflamed skin anywhere that has come into contact with the dye.
A severe reaction to PPD can cause anaphylactic shock, a life-threatening condition that requires immediate medical treatment. This can happen hours or days after using the dye, and causes symptoms including extreme swelling of the face, hands, feet, throat and tongue, difficulty breathing, vomiting, and loss of consciousness if it is not treated fast enough [6]. If you notice any of these symptoms after dying your hair, be sure to contact emergency services immediately.
If you’re still keen to dye your hair, there are several ways to reduce the likelihood of an allergic reaction. Around 38% of people report itching after using hair dye [7], suggesting an allergic reaction. Ways to prevent a reaction include [6]:
Hair dye does not stop or slow hair growth, but it can cause hair loss by damaging the colour-treated areas. Semi-permanent hair dyes reduce the tensile strength of hair with repeated use, leading to hair breakage and hair shedding [2].
If you rub or comb your hair too vigorously while dying it, the friction can cause further loss of already weakened hair. Hair dye can’t affect your hair follicles, so healthy hair should regrow once you stop using it.
The exception to this rule is hair thinning caused by contact dermatitis. Allergic contact dermatitis of the scalp can cause telogen effluvium [8], one of the most common types of alopecia, which is characterised by excessive hair shedding [9].
In rare cases, an allergic reaction to hair dye containing PPD can cause severe hair loss [10]. The photo below shows a 41-year-old woman who experienced severe hair loss after applying hair dye that contained PPD. Here is an image of her scalp 6 days after using hair dye:
And here is a photo of her scalp 2 months later, when hair loss spread to 90% of her scalp:
This patient’s symptoms improved after starting treatment with systemic steroid medication. She stopped using the hair dye, and she had no recurrence of hair loss 18 months later [10].
You should stop using your hair dye immediately if you experience significant hair loss. Significant, sudden hair shedding is often caused by an allergic reaction, which may worsen with continued use.
If you have noticeable hair thinning due to repeated dying, it may be time to take a break from colour treatment. New, undamaged hair should grow through when given time.
In the rare event that semi-permanent hair dye causes telogen effluvium, rest assured that it usually resolves on its own around 3-6 months after you start noticing hair loss [11]. Minoxidil, a medication for hair loss, may also help to speed up recovery from telogen effluvium [12].
It can be hard to know whether your hair loss is related to semi-permanent hair dye or if it has an entirely different cause. And common forms of alopecia, such as male pattern baldness or female pattern baldness, can progress if left untreated. So while some hair loss in the shower is normal, if you have concerns, it is best to book a consultation with a trichologist just to be on the safe side.
They can diagnose the first signs of hair thinning and balding and identify what is causing your symptoms. Once the cause of your hair loss is determined, they will provide you with the best, personalised treatment recommendations to help you achieve hair regrowth.
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