> ## Documentation Index > Fetch the complete documentation index at: https://docs.hi-doctor.ai/llms.txt > Use this file to discover all available pages before exploring further. # Hydroquinone — how it lightens, and its limits > Hydroquinone 4% is the reference topical for melasma. How it inhibits tyrosinase, why it is used in defined courses, and the ochronosis risk behind that rule. Hydroquinone is the long-standing reference topical for melasma and other forms of epidermal hyperpigmentation. It works, it is prescription-only in the EU, and it comes with a specific rule about how long it should be used for — a rule that exists because of a well-documented adverse effect of prolonged uninterrupted use. ## What it is Active ingredient: **hydroquinone**. On this service it is prescribed at **4%** as a cream or a gel on the [melasma](/library/conditions/melasma) pathway, and as the 4% component of the compounded melasma combination formula alongside [tretinoin](/library/medicines/tretinoin) 0.025%, kojic acid 2% and [niacinamide](/library/medicines/niacinamide) 4%. In the EU it is marketed under brand names including HQUIN and Licoforte. Hydroquinone was removed from over-the-counter cosmetic use in the EU and is available only on prescription. That is not a formality — the two adverse effects that matter most with hydroquinone both come from unsupervised, prolonged, high-concentration use. ## How it works Hydroquinone is a competitive inhibitor of tyrosinase, the rate-limiting enzyme that converts tyrosine to DOPA and then to dopaquinone at the head of the melanin synthesis pathway. Blocking that step reduces the amount of melanin the melanocyte can produce. It has a second, less-discussed action: it is cytotoxic to melanocytes at higher concentrations and with prolonged exposure, causing degradation of melanosomes and damage to the melanocyte itself. That component of its effect is why prolonged use is not benign, and it is the reason courses are time-limited rather than open-ended. Melanin sitting in the upper layers of the skin responds far better than pigment that has dropped into the dermis. That distinction is normally made with a Wood's lamp in person, and it is one honest limitation of assessing melasma from a photograph. Hydroquinone reduces melanin production while ultraviolet and visible light stimulate it. Without daily broad-spectrum protection the treatment is being undone as fast as it works, which is the most common reason a course fails. ## Why courses are time-limited **Exogenous ochronosis.** Prolonged, uninterrupted use of topical hydroquinone — particularly at higher concentrations, over years, and especially without sun protection — can produce a paradoxical blue-black or grey-brown discolouration of the treated skin. It is caused by accumulation of ochronotic pigment in the dermis, it is difficult to treat, and it can be permanent. It is the single reason hydroquinone is prescribed in defined courses with breaks rather than continuously, and the reason the melasma questionnaire has a dedicated hydroquinone-history step. The course length, and whether a course is appropriate at all given your previous exposure, is a decision the reviewing doctor makes. Continuing a course beyond what was prescribed, or restarting one without review, is the behaviour the rule exists to prevent. ## What has been reported | Reported effect | Character | | ------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Erythema, stinging and dryness | Common, especially in the first weeks | | Irritant contact dermatitis | Common enough to matter, and consequential — irritation in pigment-prone skin can itself produce post-inflammatory hyperpigmentation, darkening the very area being treated | | Allergic contact dermatitis | Less common; an intensely itchy, spreading, worsening reaction rather than simple stinging | | Halo hypopigmentation | Lightening of the normal skin surrounding the treated patch, producing a visible ring. More likely where the product is applied beyond the patch | | Exogenous ochronosis | Covered above; associated with prolonged uninterrupted use | | Nail discolouration | Reported where the product reaches the nail folds | Test on a small area first is standard practice with hydroquinone, and the reviewing doctor will usually say so. Irritation is not just uncomfortable here — in the phototypes most affected by melasma, it is a direct route to more pigment. ## Realistic timelines No visible lightening yet, and possibly some irritation. A baseline photograph taken in consistent lighting at the start is the only reliable way to judge later. The earliest point at which lightening is usually noticeable, and it is typically subtle. The usual point of assessment, and generally the region in which a defined course sits. The doctor decides the length. Maintenance moves to non-hydroquinone agents and relentless photoprotection. Relapse with sun exposure, in pregnancy or on hormonal contraception is a feature of melasma, not a failure of the medicine. ## Who it is not suitable for **Pregnancy and breastfeeding.** Hydroquinone is avoided in pregnancy and while breastfeeding, and the combination formula additionally contains tretinoin, which is not used in pregnancy at all. Pregnancy-associated melasma is generally managed with photoprotection until after delivery and breastfeeding. The pregnancy step in the melasma questionnaire is a hard gate for this reason. Also unsuitable for anyone with known hypersensitivity to hydroquinone or an excipient, anyone with existing ochronosis, and anyone whose pigmented lesion has not been established as melasma. A new, changing, asymmetric or irregular pigmented lesion needs an in-person examination with dermoscopy, not a lightening cream. ## A note on unregulated products Skin-lightening creams bought outside a pharmacy have repeatedly been found on testing to contain mercury salts, potent corticosteroids, or hydroquinone at concentrations far above anything a prescriber would use. All three cause real harm — mercury toxicity, steroid-induced skin atrophy and pigmentation, and accelerated ochronosis respectively. A prescription route exists partly to keep this medicine away from that market. ## How Hi-Doctor handles it The review is fully asynchronous — no video call, no telephone consultation. You complete the melasma questionnaire, upload the required photograph, and a registered doctor reviews the case, including your prior hydroquinone exposure, and decides. A prescription is never guaranteed; if one is not issued, the consultation fee is refunded in full. The medicine is dispensed and paid for at a pharmacy of your choosing — the [pricing page](/essentials/pricing) covers what the consultation fee includes. ## Related reading * [Melasma](/library/conditions/melasma) * [Tretinoin](/library/medicines/tretinoin) · [niacinamide](/library/medicines/niacinamide) · [azelaic acid](/library/medicines/azelaic-acid) * [Skin ageing](/library/conditions/skin-ageing) — the photoageing that usually accompanies melasma * [How to apply a prescription topical](/library/guides/how-to-apply-topicals) * [Side effects of dermatology topicals](/library/guides/side-effects-dermatology) * [Safety and eligibility](/essentials/safety) ## Start a consultation Answer the melasma questionnaire and upload the required photograph. A registered doctor reviews it and decides whether a topical treatment is appropriate — declining is a normal outcome. See [what it costs](/essentials/pricing) and [how the review works](/essentials/how-it-works). This page is reference information, not medical advice and not a prescription. Whether a medicine is appropriate for you is decided by a registered doctor after reviewing your consultation.