During pregnancy, a woman may develop one of four skin rashes that occur only during gestation. These rashes have their own unique characteristics, but share a tendency to spread and to cause itchiness of the skin.

The four major types of skin rash associated with pregnancy are:

• Pruritic urticarial papules and plaques of pregnancy (PUPPP). A rash that typically begins as small raised bumps (papules) within the stretch marks on a woman’s abdomen. It is the most common skin rash that occurs during pregnancy, affecting between one in 160 and one in 300 pregnant women.
  
  
• Prurigo of pregnancy. A rash linked to abnormal blood hormone levels, particularly elevated levels of gonadotropins and lower levels of cortisol and estrogen. This type of skin rash affects between one in 300 to one in 450 pregnant women.
  
  
• Pruritic folliculitis of pregnancy. A condition so similar to prurigo of pregnancy that some experts do not distinguish between the two types of rash. This rash resembles steroid-induced acne and most often affects the trunk of a woman’s body. The incidence of pruritic folliculitis of pregnancy is unknown.
  
  
• Pemphigoid gestationis. A blistering disease that occurs in one in every 1,700 to one in every 50,000 pregnant women.

In rare cases, pregnant women may experience severely itchy skin that is not accompanied by a rash. This is known as intrahepatic cholestasis of pregnancy (ICP). This condition interferes with liver function and may be fatal for a fetus. It is sometimes accompanied by mild jaundice (yellowing of the skin and whites of the eyes).

The cause of skin rashes associated with pregnancy is not always clear, although theories have been suggested. By their very nature, these skin rashes affect women only during their reproductive years.

In diagnosing a skin rash associated with pregnancy, a physician will likely ask the patient about the history of the rash (including when and where it first erupted) and symptoms associated with it. A skin biopsy may be ordered to help the physician pinpoint the exact nature of the lesions.