Fact-check Friday: What’s wrong with hydroquinone?

This week’s Fact-check Friday (it’s late, I know, sorry!) looks at another controversial ingredient, hydroquinone. What is it, what does it do, why do people say it’s bad, and is it actually bad? Let’s find out…

What is hydroquinone?

Hydroquinone (sometimes referred to as “HQ”) is a chemical with the structure shown below:

It occurs naturally in small quantities in things like fruits, beer, coffee, and various animal products too.

What does it do?

Hydroquinone is the gold standard for getting rid of uneven dark patches in the skin (hyperpigmentation), which are areas with more melanin than normal. Many different conditions can cause these patches, including hormone-related melasma, trauma-indiced post-inflammatory hyperpigmentation (PIH – such as dark marks from acne) and sun damage.

The main way hydroquinone does this is by slowing down melanin production by cells called melanocytes in the skin. The first step in the formation of melanin involves the transformation of the amino acids tyrosine and L-DOPA into dopaquinone, performed by an enzyme called tyrosinase.

Since hydroquinone is shaped a bit like tyrosine and L-DOPA, having it around means the tyrosinase will accidentally grab a hold of the hydroquinone instead of the tyrosine, and as a result melanin is made more slowly. It’s kind of like if someone keeps cramming balls of paper in your mouth, it’ll take ages to eat your lunch! (This may be the focus of my upcoming blockbuster diet book, keep an eye out.)

Concentrations of 2-4% hydroquinone in a topical cream (that’s cream you rub on your skin) are effective at reducing hyperpigmentation. It’s also a potent antioxidant.

Why are people making a fuss about it?
Due to some concerns about safety, hydroquinone is now prescription-only in many countries such as those in the EU, and the FDA has been considering a similar restriction in the US. Its use is also strictly controlled in many African and Asian countries.

Is it safe?

There are a number of areas of concern with the use of hydroquinone, ranging from scary to not-so-scary:

Carcinogenic activity

Several studies on rats reported that rats fed or injected with large amounts of hydroquinone were found to have more tumours. However, no link has been found between hydroquinone and cancer in humans. This may be due to the very different ways human and rat livers handle hydroquinone.


A very rare side effect of hydroquinone is ochronosis, a condition where there’s even darker hyperpigmentation. It more commonly in develops in people with darker skin. However, cases of ochronosis usually involves  prolonged use of hydroquinone, or the use of high concentrations. Some cases are also possibly due to other, more dangerous, illegal skin bleaching ingredients in the treatments, such as mercury compounds and glucocorticoids – very few reported cases involved hydroquinone treatments from well-regulated markets.

Skin sensitivity

Hydroquinone can be harsh on skin. A significant proportion of people are allergic to it, and in others it can cause irritant contact dermatitis (itchiness and redness), which may require a steroid cream to be used in conjunction with the hydroquinone treatment.

During and after hydroquinone treatment, skin is more vulnerable to UV rays, meaning extra sun protection measures are needed to prevent skin damage, skin cancer or rebound hyperpigmentation.

Destruction of melanocytes

One issue with hydroquinone doesn’t really come from hydroquinone itself – it’s the fact that it slowly reacts with oxygen to form chemicals like p-benzoquinone and hydroxybenzoquinone, which can kill melanocytes, the cells that make melanin. Unlike the action of hydroquinone, this actually leads to (usually uneven and unattractive) skin bleaching. You can avoid this side effect by throwing away the cream if it becomes discoloured (hydroquinone creams slowly turn yellow-brown over time), and by using products that come in air-tight pump bottles.

Are there alternatives?

There are quite a few alternatives on the market now – I’ll be writing about them in the very near future. These include retinoids,  azelaic acid, arbutin, kojic acid, licorice extract, vitamin C and N-acetyl glucosamine. A few of these also work to enhance the action of hydroquinone, which means you can use less of it (reducing potential side effects) and still get excellent results.

Bottom line: Hydroquinone is not as scary as you might think, from all the fuss about it! It’s the best pigmentation-reducing ingredient on the market; however, there are still some possible side effects, which can be reduced by using hydroquinone in smaller quantities, in conjunction with other products. There are also safer alternatives available, even though they’re less effective.

Further reading

ZD Draelos, Skin lightening preparations and the hydroquinone controversy, Dermatologic Therapy 2007, 20, 308.

TS Poet, H Wu, JC English and RA Corley, Metabolic rate constants for hydroquinone in F344 rat and human liver isolated hepatocytes: application to a PBPK model, Toxicol Sci 2004, 82, 9.

CB Lynde, JN Kraft and CW Lynde, Topical treatments for melasma and postinflammatory hyperpigmentation, Skin Therapy Letter, 2006, 11, 1.


  1. says

    I have some hydroquinone cream (it’s available OTC in pharmacies here in NZ) that I bought to fade some post-acne hyperpigmentation, but have been too scared/too much of a product hussy to bother using it. There is a weird scab thing on my arm though that I should really try it out on. Interesting what you said about certain ingredients that potentiate the action of hydrouinone too — will look into that. Thanks for the writeup!

    • says

      It’s one of those seemingly unavoidable things about pharmacology – the more effective something is, the more likely there’ll be severe side effects! Fixing hyperpigmentation is one of those things where there’s no perfect answer yet.

  2. says

    Thanks for the thoughtful and well-written article. Hydroquinone’s kind of the gold standard for hyperpigmentation treatment right now due to how effective it is, but like you mentioned, a lot of the “best drugs” come with scary side effects. That’s just the compromise that people have to make in using it. Of course, it’s best to try and treat conditions like acne and prevent sun damage before scarring/pigmentation occurs in the first place.

  3. says

    Hey LabMuffin!

    I’m just a little unsure about how to use a 2% hydroquinone product I recently purchased from Paula’s Choice (the one combined with salicylic acid). I have discolouration from previous acne spots in the “triangle” region of my face, but not necessarily extending to the perimeters of my face. Is it ok to use the product all over the skin, or is it better as more of a spot treatment? Thannnks!!!

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