Patchy skin color refers to areas of irregular skin coloring. Mottling or mottled skin refers specifically to blood vessel changes in the skin which cause a patchy appearance.

Irregular or patchy discoloration of the skin can be caused by:

• Changes in melanin, a substance produced in the skin cells that gives skin its color
• Growth of foreign organisms on the skin
• Blood vessel (vascular) changes

The following can increase or decrease melanin production:

• Your genes
• Heat
• Injury
• Exposure to solar or ionizing radiation
• Exposure to heavy metals
• Changes in hormone levels

Exposure to sun or ultraviolet (UV) light, especially after taking a medicine called psoralens, may increase pigmentation. Increased pigment production is called hyperpigmentation.

Decreased pigment production is called hypopigmentation.

Skin color changes can be a single disorder, or they may result from other medical conditions or disorders.

How much skin pigmentation you have can determine, to some extent, which skin diseases you may be more likely to develop. For example, lighter-skinned people are more sensitive to sun exposure and damage, which raises the risk for skin cancers. However, too much sun exposure can lead to skin cancers even in darker-skinned people. See:

• Basal cell carcinoma
• Squamous cell carcinoma
• Melanoma

Generally, pigment changes are cosmetic and do not affect physical health. However, psychological stress can occur because of pigment changes. Some pigment changes may be a sign that you are at risk for other medical disorders.

• Cafe-au-lait spots
• Chloasma
• Cuts, scrapes, wounds, insect bites and minor skin infections
• Erythrasma
• Melasma
• Melanoma
• Moles (nevi), bathing trunk nevi, or giant nevi
• Mongolian blue spots
• Photosensitivity as a reaction to medications or certain drugs
• Pityriasis alba
• Radiation therapy
• Rashes
• Sunburn or sun tan
• Tinea versicolor
• Uneven application of sunscreen resulting in areas of burn, tan, and no tan
• Vitiligo