Hydroquinone is an aromatic chemical compound, a metabolite of benzene.

Hydroquinone is a skin-lightening agent used to reduce melanin production, the pigment responsible for skin color. It is commonly used in products to treat hyperpigmentation such as dark spots, melasma, and freckles.

Chemical Composition and Structure:

• Components:
  • Hydroquinone: A phenolic compound with two hydroxyl groups ortho to the carbonyl group.
• Structure:
  • Molecular Formula: C6H6O2
  • Molecular Weight: 110.11 g/mol
  • Chemical Structure: Hydroquinone is an aromatic compound with two -OH (hydroxyl) groups attached to a benzene ring at positions 1 and 2.

Physical Properties:

• Appearance: White crystalline powder.
• Odor: Odorless or slightly characteristic.
• Solubility: Soluble in water, ethanol, and acetone.
• Texture: Fine powder with a smooth texture.

Production Process:

1. Synthesis: Hydroquinone is produced synthetically through various chemical processes, including the treatment of phenol with oxidizing agents.
2. Purification: The raw material is purified through crystallization or other methods to ensure high purity.
3. Formulation: It is incorporated into cosmetic formulations at concentrations typically ranging from 0.5% to 2%.

Applications:

• Skin Care: Used in serums and creams to lighten dark spots, melasma, and hyperpigmentation. It reduces hyperpigmentation by blocking the activity of tyrosinase, a key enzyme in melanin production.
• Dermatological Treatments: Used in prescribed treatments for pigmentation issues.
• Lightening Cosmetics: Used to even out skin tone and enhance clarity.

Environmental and Safety Considerations:

• Environmental Impact: The production of hydroquinone can have environmental impacts if not managed properly. Sustainable and controlled production practices are important.

Cosmetics -INCI Functions

Antioxidant agent. Ingredient that counteracts oxidative stress and prevents cell damage. Free radicals, pathological inflammatory processes, reactive nitrogen species and reactive oxygen species are responsible for the ageing process and many diseases caused by oxidation.

Bleaching agent. This ingredient exerts a depigmentation and/or lightening action on the set of pigments produced by melanocytes and known as melanin, the substance responsible for skin colouration.

Fragrance. It plays a decisive and important role in the formulation of cosmetic products as it provides the possibility of enhancing, masking or adding fragrance to the final product, increasing its marketability.  The consumer always expects to find a pleasant or distinctive scent in a cosmetic product.

Hair dyeing. It is an ingredient that adds a colouring to the hair that can be temporary, semi-permanent or permanent depending on what other ingredients are added to achieve the result. The pH for hair dyeing is generally between 9 and 10.

Reducing agent. Ingredient that facilitates permanent hair waving by adjusting the pH to an optimal level.

Cosmetic safety

Restricted cosmetic ingredient as II/1339 III/14 a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported:  1,4-Dihydroxybenzene (Hydroquinone), with the exception of entry 14 in Annex III

Safety

It is a toxic agent and can promote the growth of cancer cells.

Enguita, F. J., & Leitão, A. L. (2013). Hydroquinone: environmental pollution, toxicity, and microbial answers. BioMed research international, 2013.

Abstract. Hydroquinone is a major benzene metabolite, which is a well-known haematotoxic and carcinogenic agent associated with malignancy in occupational environments. Human exposure to hydroquinone can occur by dietary, occupational, and environmental sources. In the environment, hydroquinone showed increased toxicity for aquatic organisms, being less harmful for bacteria and fungi. Recent pieces of evidence showed that hydroquinone is able to enhance carcinogenic risk by generating DNA damage and also to compromise the general immune responses which may contribute to the impaired triggering of the host immune reaction. Hydroquinone bioremediation from natural and contaminated sources can be achieved by the use of a diverse group of microorganisms, ranging from bacteria to fungi, which harbor very complex enzymatic systems able to metabolize hydroquinone either under aerobic or anaerobic conditions. Due to the recent research development on hydroquinone, this review underscores not only the mechanisms of hydroquinone biotransformation and the role of microorganisms and their enzymes in this process, but also its toxicity.

Chemical name    benzene-1,4-diol

CAS: 123-31-9

EC number 204-617-8

Molecular Formula  C₆H₆O₂ or C₆H₄(OH)₂