Hydroquinone Dangers

Hydroquinone is banned in Europe because of the side effects.  It contains Mercury and after long term use it will cause kidney and liver damage.  Once you stop using hydroquinone your suppressed melanin cells (melanocytes) will go into overdrive causing more pigmentation. 
ne woman used it on her face for months.  She stopped using it after she got the desired results and her skin on her face got 3 shades darker.
Products containing up to 2 percent Hydroquinone were legally available in the UK until 2001 when the Department of Trade and Industry (DTI) issued the draft 24th Commission Directive. This bans preparations with Hydroquinone due to the long term effects as it accumulates in the tissues. The UK Cosmetic Product Regulations 1978 prohibits the use of Mercury compounds.

Stay away from products that have hydroquinone but if at all you must use any product with a certain percentage of hydroquinone, maybe to treat a certain problem, make sure it is recommended by a skin specialist and it should be for a time and you stop it. You don’t use hydroquinone for a long time. The problem is that a lot of people would just continue to use the product for years.   
Hydroquinone is a possible carcinogen and has been linked with disfiguring condition called ochronosis that causes darkening and thickening of the skin, along with raised bumps and greyish-brown spots.