Hydroquinone functions by inhibiting the activity of tyrosinase, the enzyme necessary for melanin production. The 4% concentration is a potent formulation typically reserved for cases that do not respond to lower strengths. Because of its potency, it is often used in cycles under medical supervision to prevent complications. Safety Concerns and Side Effects

Hydroquinone is a topical skin-bleaching agent used in the treatment of hyperpigmentation conditions such as melasma, solar lentigines (age spots), and post-inflammatory hyperpigmentation. While it is a widely recognized treatment, the use of higher concentrations, specifically 4%, involves significant medical considerations. Mechanism and Efficacy

Using this strength without a professional diagnosis can mask other skin conditions, including skin cancer. Professional Consultation

The use of 4% hydroquinone is associated with several potential side effects, ranging from mild irritation, redness, and dryness to more severe reactions. A primary concern with long-term or unsupervised use is exogenous ochronosis, a condition characterized by blue-black darkening of the skin that can be permanent. Due to these risks, many regulatory bodies, including the FDA in the United States, have classified hydroquinone as a drug that requires a prescription and professional oversight. Risks of Unregulated Online Purchases