Antihistamines are prescribed for a variety of conditions, including:

• Allergies. Most allergy symptoms, including runny nose and sneezing can be effectively treated by taking an antihistamine before or during the reaction. Allergies are triggered by a variety of allergens (e.g., pollen, dander, mold, food). Conditions caused by allergic reactions to these substances are all treated with antihistamines. These include:
  
  
• • Allergic rhinitis. Also known as hay fever, antihistamines are effective at treating the congestion and itchy eyes associated with this condition.
    

    
    

  • Allergic conjunctivitis. This inflammation of the tissue on the inside of the eyelid can be reduced using antihistamines.

    

  • Allergic sinusitis. Antihistamines can reduce the inflammation of the lining of the sinus cavities that occurs with sinusitis.
    
    

    

  • Hives. These red, swollen patches of skin that often itch or burn can be treated with an antihistamine.
    

    

    
    

  • Anaphylactic shock. This potentially life-threatening condition involves difficulty breathing and a drop in blood pressure as the result of exposure to an allergen. These severe reactions typically require a shot of epinephrine to treat symptoms; however physicians may recommend that patients take antihistamines following an injection of epinephrine. Although antihistamines cannot stop an anaphylactic reaction, they can reduce the severity of symptoms. Patients prone to anaphylaxis may be instructed by their physician to include antihistamines in their allergy kit. Individuals who are susceptible to anaphylaxis and unresponsive to epinephrine may also find antihistamines useful. However, antihistamines cannot reverse anaphylaxis and are not a substitute for epinephrine.
    
     
• Atopic dermatitis. This is 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.
  
  

  

• Contact dermatitis. Inflammation that occurs on the skin’s surface after coming into contact with an allergen or irritant. Over-the-counter antihistamine lotions may be applied directly to the skin to relieve itching associated with contact dermatitis. Prescription antihistamines may be used if over-the-counter antihistamines do not relieve the itching.  
  
  
• Angioedema. A condition in which the skin swells and welts form on the skin, usually near the eyes, mouth, hands, feet and genitals. Over-the-counter antihistamines may help relieve minor symptoms of angioedema.  
  
  
  
  
• Cold and flu symptoms. These include coughing, runny nose and watery eyes.
  
  
• Sleeplessness. The drowsiness caused by many types of antihistamine can be used as an effective sleep aid.
  
  
• Motion sickness, dizziness, nausea and vomiting. Antihistamines are able to block certain signals to the brain and can reduce these kinds of symptoms.
  
  
• Nervousness and anxiety (these symptoms are usually treated with doxepin or hydroxyzine).
  
  
• Parkinson’s disease. In these patients the drug will sometimes decrease stiffness and tremors.