When the skin receives an injury, such as a cut or a scratch, the resulting inflammation often sends the skin's pigment-producing cells---the melanocytes---into overdrive. Consequently, once the wound heals, it sometimes leaves behind a patch of darker skin that dermatologists refer to as post-inflammatory hyperpigmentation. While the condition is not dangerous and will likely fade on its own with time, the use of a topical skin bleaching cream, such as hydroquinone, can help speed up the process. Hydroquinone lightens skin discolorations by blocking tyrosinase, an necessary enzyme for the production of melanin.
Talk to your dermatologist about the side effects associated with hydroquinone. While most users tolerate the medication well, some mild side effects, such as redness, itching or stinging, can occur. These symptoms are usually temporary. On rare occasions, some people experience an allergic reaction to hydroquinone that can produce severe burning, itching or swelling of the treated area.
Obtain a prescription from your dermatologist for topical hydroquinone cream. The prescription-strength topical cream contains up to 4 percent hydroquinone. However, over-the-counter varieties are available, as well, that contain up to 2 percent. If you choose the over-the-counter product, the American Academy of Dermatology advises that you only purchase it if the hydroquinone percentage is clearly indicated on the package, since higher doses can cause adverse effects.
Test for hydroquinone sensitivity. DermNet NZ recommends that you conduct a patch test before using a hydroquinone medication to ensure that you won't experience an allergic reaction. Apply a small amount of the cream to the hyperpigmented area and wait 24 hours. If no redness, itching or other reactions occur, begin using the cream.
Apply a thin layer of the hydroquinone cream twice daily to clean skin. Cover only the pigmented area, as the cream will also lighten the unaffected area. Wait a few minutes to allow the skin to absorb the medication before applying lotions or sunscreen. Expect to see a lightening of the scratch mark after approximately four weeks of use. Do not use hydroquinone for longer than six months.