We use topical hydroquinone in concentrations of 2-12% for skin pigmentation and it is very safe. There is a problem with irritation that may occur idiosyncratically at the higher strengths. Also, long term usage is discouraged because of the risk of exogenous ochronosis (increase in pigment) but is infrequently seen in practice because a prescription is needed in the US for compounds 4% and greater. Hope this helps.

Hydroquinone is a safe molocule with mild long term use adverse reactions such as ochronosis (Mud like pigmentations) specially with higher doses 4% or more but with ususal dose 2% rarely might cause any harm specialy if used togather with other molecules as retenoids and low grade steroids in some formulae.

I think that hydroquinone is a safe product.

"In 1994, the Journal of the American College of Toxicology (now known as the International Journal of Toxicology) published “The Addendum to the Final Report on the Safety Assessment of Hydroquinone.” Its conclusion stated that “hydroquinone is a potent cytotoxic agent that causes mutations and alterations to DNA, and that it should not be used in any leave-on type of product; it is safe for rinse-off products when used in concentrations less than 1%.” http://www.skininc.com/skinscience/ingredients/41973632.html

Read also this: even the FDA is taking notice, although they are notoriously slower than EU authorities at regulating these;

http://www.cosmeticsandtoiletries.com/regulatory/region/northamerica/3874572.html

It is banned in the EU. I would think about it twice before using it.

 Alice thanks for refered lnformation I will read it carefuly as a new add to my knowledge.Thanks again.

There are also many articles to the contrary that support clinical safety of the compound when used as a topical preparation. Informed patients and physicians can weigh the risk/benefit and make personal decisions about it. 

What we do know from studies is that activation of toxicity has been demonstrated in research animals after metabolism in the liver at very high doses of hydroquinone which could never be achieved after topical application.

So I would say: DONT EAT IT or don't feed it experimental animals! 

This is a review article and the abstract: 

The safety of hydroquinones, JJ Nordlund1, PE Grimes2,* andJP Ortonne3, Journal of the European Academy of Dermatology and Venereology

Volume 20, Issue 7, pages 781–787, August 2006

Abstract:

Hydroquinone is one of the most effective molecules for the treatment of hyperpigmentary disorders, with over 40 years of efficacy and safety data. Concerns over its safety have been raised because of the fact that it is a derivative of benzene and because of the long-term side-effects observed with cosmetic products containing high concentrations of hydroquinone. However, despite 40–50 years use of hydroquinone for medical conditions, there has not been a single documented case of either a cutaneous or internal malignancy associated with this drug. This article reviews the evidence for the safety of hydroquinone in the treatment of hyperpigmentation conditions.

For those who believe that the government knows what is best for them; they can try to treat this difficult problem with other means that may be less effective and more expensive.

Personal bias comes to mind when I consider the statement that  "FDA is notoriously slower than the EU in regulating these".  It seems to me that this the FDA's "lack of regulation" can be viewed positively as well. It has been more than 6 years since the FDA began looking at the issue and no regulation has been made. Does this support its' safety? maybe, maybe not . But many physicians and patients are grateful to have the opportunity to make our own educated decisions as to whether to apply this to our own skin.

 Drug safety and personal experience should always been tken in consideration to make the right decision for the benefit of the patient.

Dr Luciann Thank you very much for that interesting post. Old guard Hydroquinone must have stood the test of time. the new molecules like oligopeptide 34 is supposedly expensive and the results are being awaited.

Misuse of hydroquinone is more frequent which has resulted in the companies looking for alternatives.

I believe the subtitle of that question was: "Safety of hydroquinone in the context of extensive and unmanned usage and production of cosmetic products sold as skin lighteners." It is in that context that I answered. Not in the context of prescribed use for actually sick patients. The compulsion to whiten skin, largely fueled by media and advertising practices, along with cultural factors, has driven many to use whatever is available without any regards for the benefit/risk ratio. I was going to make sure everyone understood my answer in that context because I thought the question might be directed at dermatologists and clinical practitioners after reading Luciann's answer. It is not the case and I maintain that the use of hydroquinone for cosmetic purposes is both dangerous and irresponsible. There might also be effects which we may not master today, such as subclinical inflammation, triggering accelerated aging of the skin in the long run. Someone with healthy skin should turn to milder forms of skin lightening. Or try and prevent age spots by controlling inflammation better throughout life. As far as just lightening dark skin, it is just not a good idea, even from a basic sociological standpoint, to encourage these practices.

I often wonder if I am mindlessly biased against Hydroquinone and that is why I see the complications.   I know some patients who have had great success with hydroquinone and their pigmentation has disappeared.  On the other hand I know patients who have used hydroquinone and their pigmentation disappears and then as they start tailingoff the treatment with the standard Kligman formula, the pigmentation returns and so they fall into a cycle of treating and trying to stop and eventually some stop and the pigmentation gets worse and gets much worse than before they started.   Then I have found that these patients seem to have "rogue" melanocytes and it is very difficult to get them to stop producing melanin.   I don't prescribe hydroquinone and I recommend everyone to avoid using it even in low doses.   It can be a cellular toxin at low doses.  I do not believe that ochronosis is a "mild" side effect.   Why do I see the problems and the dermatologists who prescribe the hydroquinone mixtures don't?  Are their patients walking away from them and specifically coming to me? In South Africa cosmetics may not contain Hydroquinone, but doctors are permitted to prescribe Hydroquinone usually in the Kligman formula with Retinoic acid and hydrocortisone. I guess the complication rate of hyper-pigmentation after using hydroquinone may be as high as 40% but this is a thumbsuck.  I believe that people have forgotten the central role of retinoids in minimising pigmentary disorders.  Nourish skin with vitamin A and that will reduce the development of pigmentary blemishes.  Use alternatives to Hydroquinone. 

Miss use of hydroquinone could be a patient or others like those who pretending that they are making formulae for treating skin like pigmentatons specially in third world and spcifically in black races as such a phenomena is widespead and they have a lot of customers and so you may see a lot of complicated cases a problem that go side by side with topical steroids miss use.