Hydroquinone based products are widely used. Hydroquinone is very effective in reducing hyperpigmentation. It works by inhibiting the tyrosinase enzyme, thereby preventing the production of melanin. Usually, hydroquinone treatments require several weeks before any significant improvement in the hyperpigmentation (up to six months). Most dermatologists recommend 4% hydroquinone products, only available by prescription. Hydroquinone with up to 2% concentration is available over-the-counter. It has some potential side effects, such as irritation, allergy, and nail discoloration.
Hydroquinone has also been reported to cause ochronosis, a bluish-black discoloration of tissue. This side effect is relatively rare with short-term use of low-to-medium concentrations. However, it appears to be relatively frequent after prolonged use of high concentration (5% or more), especially in dark-skinned people.
Some studies with mice indicate that high dosis of hydroquinone can cause cancer. However, more research is needed in order to better evaluate those results.
Retinoids reduce hyperpigmentation by accelerating cellular turnover and increasing epidermal exfoliation, which leads to a greater loss of epidermal melanin. Retinoids may also reduce melanin synthesis because when speeding up exfoliation melamine has less time to be produced.
Alpha hydroxy acids (i.e., glycolic acid) speeds up the turnover of epidermal cells and accelerates exfoliation, causing more melanin to be removed.
Glabridin (also known as licorice extract) inhibits melanin production by inhibiting tyrosinase activity. It also has anti-inflammatory properties. However, at the time of this writing, there are no clinical studies as to how glabridin compares to the more established skin lighteners or what its optimal concentrations may be.
Kojic acid is a natural product found in a type of fungi and produced in the fermentation process of rice to make sake. It seems to inhibit melanin production by blocking an enzyme essential to its production.
Kojic acid’s major drawback is that it can cause skin sensitivity and contact dermatitis in some individuals. This may manifest as redness, rashes or even blisters.
Azelaic acid is a component of grains, such as rye, barely, and wheat. Besides being used to treat hyperpigmentation, it is also effective against acne. It is antibacterial, anti-inflammatory and will protect against free radicals too.
Arbutin is a natural and safe hydroquinone derivative. It is found in the leaves of some berry plants.
It has been shown that arbutin is an effective inhibitor of melanine production by blocking Tyrosinase activity.