A wide range of dry shampoos are available on the market that claim to absorb excess oil from the scalp or hair and remove bad odour. Consumers who cannot lather with water, such as new mums during postpartnum recovery, wild campers or after working out, might opt for dry shampoos in hopes of immediately alleviating greasy and flat hair, and restoring freshness and volume. In view of the large-scale product recall that happened overseas due to high concentrations of the carcinogen benzene detected in certain products, the Consumer Council examined the labelling information of 21 models of dry shampoos available in Hong Kong and reviewed some overseas study reports, and found that aerosol products may have potential risk of benzene contamination due to the use of LPG components. In addition, over 60% were labelled as containing denatured alcohol/alcohol, generally with a relatively high concentration (listed as the 2nd to 5th ingredient in the ingredient list), which might lead to dry hair when used excessively. Moreover, over 50% were labelled to contain fragrance allergens, with a model labelled with as many as 8 types of fragrance allergens, thus consumers who are allergic to fragrances need to pay special attention. The Council reminds consumers that dry shampoo products are temporary reliefs that do not remove grease and dirt like shampoo with water, and that prolonged use may cause inflammation or affect hair growth. As such, consumers should choose and use such products with care.
The Council examined the labelling information of 21 models of dry shampoos, including 11 aerosol sprays, 4 powder or powder sprays, and 6 liquid sprays, gels, or mousses, priced from $15 to $410 per bottle. 3 models were in travel size, which were smaller in volume than similar products.
Aerosol Products May Contain the Carcinogen Benzene
Must Be Used with Caution
In 2022, a US study revealed that among 148 different batches of dry shampoo samples from 34 brands, over 70% were found to contain detectable levels of benzene in the first spray. In the same year, another study in New Zealand pointed out that benzene contamination would be more common in products containing propane, butane, isobutane, or hydrofluorocarbon (HFC)152a as propellants, and that such aerosol propellants were also commonly used in dry shampoos. Although benzene is not intentionally added as an ingredient in the manufacturing of cosmetic products, as benzene is naturally present in crude oils, its presence in dry shampoo products might be technically unavoidable as a result of solvent residual or impurities in the propellant. When such products are used, benzene may also be emitted in addition to LPG.
Benzene is volatile, with slightly sweet odour, naturally occurring as a component of crude oils and gasoline. However, as fragrance is often added into aerosol products, it is not easy to distinguish by smell whether benzene has been released. Benzene is easily absorbed by the skin and may enter the body through skin contact and inhalation, and is classified as carcinogenic to humans by the International Agency for Research on Cancer (IARC). Short-term inhalation of benzene can cause drowsiness, dizziness, and irritation to the eyes, skin, and respiratory tract. Long-term exposure may increase the risk of anaemia and leukaemia.
In addition, cyclosiloxane compounds including cyclopentasiloxane (D5) and/or cyclohexasiloxane (D6), despite being an ideal hair conditioning agent with anti-static function, they can last in the environment for extended periods, and are bioaccumulative, and D5 is a suspected endocrine disruptor.
Among the models examined by the Council, all 11 aerosol products were labelled as containing LPG components such as propane, butane, isobutane, or HFC 152a, while 4 of these were labelled as containing cyclosiloxane compounds D5 and/or D6. Overseas study revealed that not all aerosol products were found to contain high concentrations of benzene, and according to the Council’s study this time, not all aerosol products were labelled to contain cyclosiloxane compounds. Although there is no evidence to suggest harm to human health through occasional use of dry shampoos, for safety and environmental reasons the Council recommends consumers to minimise the use of aerosol products which contain LPG components and cyclosiloxane compounds, and to switch to alternatives with simple formulation.
Over 50% Labelled as Containing Alcohol and Fragrances/Fragrance Allergens Prolonged Use Might Cause Various Side Effects
To make hair appear less greasy, absorbents such as rice starch and corn starch are the major components of dry shampoos to absorb oils. Besides, many models were also labelled to contain fragrance and alcohol. The former helps to cover bad odour while the latter helps disperse the absorbent, dissolve grease, and remove odour.
Over 60% (13 models) were labelled to contain denatured alcohol/alcohol, and relevant ingredient were generally listed more prominently in the ingredient lists (listed as the 2nd to 5th ingredient in the ingredient list) reflecting a higher concentration. An overseas study showed that the maximum concentration of alcohol in dry shampoos could be as high as 30%. Exposure to high concentrations of alcohol may damage the natural protection barrier of the skin, and if oil on hair is excessively removed, the hair may become brittle and lack lustre.
Among all models, 14 were labelled as containing fragrances, of which 11 were labelled as containing 1 to 8 types of fragrance allergens, while 2 were labelled as containing 7 to 8 types of fragrance allergens. As such, individuals with allergic reactions to fragrances or related fragrance substances should pay particular attention. Additionally, as 5 models were found to have no detailed information on ingredients, consumers would be unable to identify, through the labels, whether the product contained allergy-causing ingredients.
The US National Poison Centre opined that dry shampoos commonly contain fragrances, surfactants, and preservatives, which may cause respiratory irritation in some individuals if inhaled. If used in enclosed spaces, it may result in coughing or even breathing difficulties. The Council recommends manufacturers to switch to safer and more environmentally friendly ingredients, and to strengthen quality control measures, so as to minimise the possibility that their products would contain or release harmful substances as much as possible.
Not a Substitute for Lathering Routines
Dry shampoos can only help absorb grease from the hair, reduce the feel of greasiness and improve the appearance, but they are not a real cleansing agent and cannot thoroughly remove oil and dirt from the scalp and hair. The Council reminds consumers to maintain a habit of washing hair with shampoo and water as a personal hygiene routine. If consumers rely solely on dry shampoos for extended periods for the sake of convenience, residue of hair-styling products, dirt, and germs may be accumulated on the scalp and hair, which may in turn affect scalp health in the long run, causing inflammation or even inhibiting hair growth. Some tips for using dry shampoos:
- Regardless of which type of dry shampoo, it should be used in well-ventilated areas. Avoid using in enclosed spaces with poor ventilation, avoid spraying towards the eyes, and keep it away from food and beverages;
- Avoid prolonged and heavy use of dry shampoos with high concentration of alcohol;
- Products must be stored in a cool place, and aerosol products should be kept at below 50°C. During outdoor activities or camping, special attention should be paid to avoid placing the product near heat sources or under direct sunlight;
- Liquid products generally contain volatile and highly flammable ingredients such as alcohol or aerosol propellants. Users should stay away from open flames when using the products and before the hair is completely dry after application, so as to avoid fire hazards. Dust from powder shampoos and powder sprays can also be ignited, and should be kept away from flames when in use;
- When using aerosol products, the nozzle should be kept at a suitable distance from the hair roots, otherwise the low-temperature vapour might induce cold burns (frosties);
- Divide hair into small sections and apply product on the areas where oil is the most noticeable, apply near the hair roots or only use an appropriate amount, and refrain from excessive use.
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