Hydroquinone is a granular white solid organic compound. Its chemical formula is C6H4(OH)2, and it is industrially produced by two main methods. It also occurs naturally in multiple places, including in the defense mechanism of a bombardier beetle. It can also be found in the poodle-dog bush, and as an active toxin in the felt-ringed agaricus mushroom. The compound was found to be carcinogenic in rats—when taken orally—however there has been no research into the carcinogenic effects of hydroquinone on humans.
Hydroquinone has multiple uses across the beauty, photography and oil industries. It is used as a depigmentor in topical skin products to reduce hyperpigmentation, such as liver spots, freckles, “age spots”, and melasma. It works by blocking melanocytes, which produce melanin, which makes you the colour that you are. In photography, it is used in the development of darkroom photographs, as a developer and reducer. It is also found in oils, foods and greases as an antioxidant.
Routes of Exposure 
Hydroquinone is banned in Japan, Australia and across the European Union due to the negative medical effects from the use of hydroquinone-containing products.
In the U.S., hydroquinone is sold at two different strengths: 2% over-the-counter, and 4% with a prescription and restricted application.
Hydroquinone poisoning affects a range of systems including the integumentary, hormonal and gastrointestinal systems.
Acute Effects 
Severity of symptoms depend on the level and type of exposure.
Ingestion of hydroquinone in higher doses can cause tinnitus, dizziness, headaches, vomiting, dyspnea, cyanosis, delirium.
Ingesting large amounts of the compound can cause edema of the internal organs, convulsions and collapse.
Chronic Effects [5,6,]
Hydroquinone is toxic to multiple body systems. Long-term effects from the exposure to hydroquinone dust can include impaired vision. It has also been found that long-term use of hydroquinone topical creams has lead to ochronosis—which can result in the discolouration of the skin to a blueish-black colour. In rodents, it was found that hydroquinone—when applied dermally—increased the incidence of skin tumours.
~h2First Aid Measures 
Inhalation: Move the victim to a fresh air source and monitor their breathing. Call a doctor if symptoms persist.
Skin contact: If there is skin or hair contact, remove the victim’s clothing, and wash exposed skin with mild soap and water. Continue with a warm water rinse. Clean contaminated clothing before re-wearing. If rash or skin irritation occurs, consult a doctor.
Eye contact: Rinse eyes with water carefully for a few minutes. Remove contact lenses if present and easy to do so. Continue rinsing. If irritation persists, contact a doctor.
Ingestion: If swallowed, DO NOT induce vomiting. Rinse mouth with water and contact a medical professional.
Exposure Controls/Personal Protection 
Engineering controls: Safety showers and emergency eyewash fountains should be accessible in the immediate area of the potential exposure. Ensure there is adequate ventilation, and whenever possible, material should be handled in a laboratory.
Personal protection: Safety glasses and protective gloves should be worn. Do not eat, drink or smoke when using hydroquinone.
The Occupational Safety and Health Administration has set an 8-hour time weighted average (TWA) concentration for hydroquinone of 2mg/m³.
Safe Work Australia: Safe Work Australia has set an 8-hour time TWA for hydroquinone of 2mg/m³.