Dr Askari Townshend presents the facts about this controversial skincare ingredient
For a drug that has been used by millions of people for decades, giving great improvements to their pigmentation disorders, hydroquinone (HQ) has a bad reputation. How and why it started I’m unsure, but the two comments I often hear (in my experience, usually from those that don’t use it) is that it can cause cancer and has been banned. Neither of these is entirely true – there have been no reports or evidence of human malignancy as a result of hydroquinone use. In 2001, countries of the European Union had hydroquinone banned from over-the-counter products yet in the USA, hydroquinone is still available up to 2% over the counter.
Every so often there is a media story, quite rightly, exposing the risks of the illegal
sale of strong HQ products in the UK. Unfortunately, these are often accompanied by medical comments overstating the risks. I was recently asked to comment for Channel 4 News, but made it clear that I am a great fan of this useful medicine and would not do any more than state the facts - they found someone else. Here I present the facts without the spin.
HQ is a phenol compound known by several names including quinol and 1-4 dihydroxy benzene. It is an anti-oxidant with several uses that take advantage of it being a soluble reducing agent – it is a major component of black and white photographic developers. In dermatology, HQ has long been used to treat pigmentation disorders and is very effective in doing so. The first (and rate limiting) step of melanogenesis is the oxidation of tyrosine to dopaquinone catalysed by tyrosinase. As a tyrosinase inhibitor, HQ interferes with melanogenesis and results in a reduction of the amount of pigment (melanin) in skin.
Pigmentation disorders are common, especially in darker skin types. Excluding vitiligo, El-Essawi et al1 found that 56% of 401 Arab-Americans complained of skin discolouration. When using larger groups (1,074 and 1,000), Alexis et al2 and Dunwell et al3 found 20% and 23% complaints respectively. The most common diagnoses were post-inflammatory hyperpigmentation (PIH), melasma and solar lentigines. By far, the most common condition causing PIH is acne. At their Skin of Color Centre in New York, Alexis et al4 surveyed 1412 patients and found that acne was the most common reason for attendance, as it was for white patients, followed by dyschromia which did not feature in the top ten reasons for patients with white skin.
Dyschromia in dark skins can be difficult to treat as there is a greater risk of PIH after peel or laser treatment than when treating white skins. HQ is particularly useful in treating this patient group and is also used as a prophylactic adjunct with peels and laser to reduce the risks. It is important to treat the underlying condition (e.g. acne) before tackling the resulting dyschromia.
There are a wide range of topical lightening agents including other tyrosinase inhibitors such as retinoids, kojic acid, azelaic acid and arbutin. Many preparations combine these ingredients (and others) for greater efficacy. A Cochrane review of interventions for melasma found that: 4% HQ is more effective than 2%; combining 4% HQ with tretinoin is more effective than either alone and the addition of a mild steroid e.g. fluocinolone acetonide, is even more effective.5
There is no doubt that HQ is a potent treatment for pigmentation disorders, but what about safety? As with almost all of the topical alternatives, HQ can cause irritation and dryness. However, this is more common with tretinoin and azelaic acid.5 Advice to avoid strong sunshine and wear good quality, high protection SPF is applicable to all topical treatment. This is not just because many of them make the skin more sensitive to sunlight, but also because the sun will drive the problem of melanogenesis.
Every so often there is a media story, quite rightly, exposing the risks of the illegal sale of strong HQ products in the UK. Unfortunately, these are often accompanied by medical comments overstating the risks.
The biggest myth about HQ is that it causes cancer. As you might expect, there have been several studies (both animal and human) looking at any possible link. McGregor6 found an increased incidence of renal tubule adenomas in male rats but this was after they had been given 25 times the normal human dose (orally rather than topically). He said, “This disease is particularly prominent in male rats,” and concluded, “the increased incidence of renal tubule adenomas in HQ-dosed male rats is without human consequence.” This confirmed the conclusion already put forward by Hard et al7 and Hard.8
A real, but often overstated, risk is one of exogenous ochronosis (EO). Ochronosis refers to brownish-yellow or ochre coloured collections of pigment found in patients carrying the disease. It is an inherited condition in which the enzyme homogentisic acid oxidase is missing, allowing homogentisic acid (and its oxide alkapton) to accumulate. EO was first described in 19128 after phenol use on a leg ulcer, and presents as a blue/ black discolouration in the skin without the systemic problems of endogenous ochronosis. The blue appearance is due to the depth of the pigment (Tyndall effect). The condition can develop after topical use of HQ, phenol, resorcinol or oral anti- malarials.9