Antihistamines are prescribed for a variety of conditions. In some cases, over-the-counter versions of these drugs may provide relief. In other cases, prescription strength formulations may be necessary. Patients should not take any medication without first consulting a physician.

Many skin conditions are treated with oral or topical antihistamines. These include:

• Atopic dermatitis. An itchy inflammation of the skin, often characterized by flaking. Histamine levels appear elevated in the skin and plasma of some individuals with this condition, making an antihistamine a useful treatment.
  
  

  

• Dry skin (xerosis). Antihistamine pills may be used to treat itchiness (pruritus) associated with dry skin.
  
  
• Hives (urticaria). Red, swollen patches of skin that often itch or burn. H1 blockers are the standard medication used to treat both acute and chronic urticaria. In some cases, these drugs may be combined with H2 blockers, oral corticosteroids or tricyclic antidepressants.
  
  
• Angioedema. A condition characterized by swelling and the formation of welts (raised marks) on the skin. It is similar to hives, except the welts are larger and form at a deeper layer in the skin. Over-the-counter antihistamines may help relieve minor symptoms such as itching and swelling.
  
  
• Lichen planus. Skin disease that causes purple or reddish-purple bumps on the skin that have flat tops. Most commonly found on the inner wrists, forearms and ankles.
  
  
• Pityriasis rosea. Acute, self-limiting, inflammatory skin disease that tends to occur in adolescents and young adults, especially in the spring and fall. This scaly, reddish-pinkish rash tends to appear as a single spot on the stomach or back. Later, additional spots may appear.
  
  
• Allergic contact dermatitis. A localized rash or skin inflammation caused by direct contact with an allergen (a substance that triggers an exaggerated immune system response). Antihistamines may be used to treat rashes that occur after exposure to allergens. For instance, itchiness associated with allergic reactions due to contact with poison ivy, oak and sumac may be treated with antihistamines.
  
  
• Pruritus. The medical name for generalized itching. In some cases, antihistamines can help relieve this itching. However, there are cases where nonsedating antihistamines are of little value in relieving symptoms, such as pruritus related to atopic dermatitis. In such cases, systemic, sedating antihistamines may be required to control symptoms.
  
  
• Scabies. An intensely itchy skin condition caused by a tiny mite that infests the skin. Antihistamines are used to treat this itch, which can last for weeks after the mite has been removed.
  
  
• Insect bites and stings. Antihistamines can help relieve the pain, swelling and itchiness associated with some insect bites and stings.

In addition to skin conditions, antihistamines are the chief treatment for many allergic conditions, such as allergic rhinitis (hay fever). Antihistamines also are used to treat the following:

• Cold and flu symptoms
  
  
• Motion sickness
  
  
• Nervousness
  
  
• Parkinson’s disease (progressive nervous disease associated with the destruction of brain cells and characterized by symptoms such as muscular tremor)
  
  
• Sleeplessness