The facts -- how whiteners work

(CNN) -- Whiteners work by controlling melanin production, and lightening freckles and age spots. The amount of melanin produced determines how dark a person's pigmentation is.

There are several types of skin whiteners. Those that contain hydroquinone, which are regulated as pharmaceuticals in Hong Kong and need to be registered before being sold to consumers.

They suppress melanin production but because long-term use can lead to patchy skin it is not recommended that people use it for over a year. It can cause mild reactions such as burning sensation or skin reddening.

Other whiteners are plant-based AHA or Fruit acid face creams (such as glycolic, lactic, tartaric, malic, kojic and citric acid). They claim to lighten the complexion by peeling off dead skin cells, thus boosting moisture, smoothing fine lines and wrinkles, unblocking pores and improving skin tone and texture.

Hong Kong's Cosmetic Ingredient Panel has concluded that AHA's are safe in cosmetic products at a certain level of concentration (10 percent or less), PH value (3.5 or higher) and if they have sunscreen or if they prescribe the use of sun protection.

Compiled with help from Consumer Council of Hong Kong, Hong Kong Department of Health and a number of Hong Kong dermatologists.