As the allergic cascade progresses and histamines, leukotrienes and other chemicals are released, the body will begin to feel the symptoms normally associated with an allergy. The histamines are usually responsible for most of the symptoms, though leukotrienes are known to contribute by aggravating inflammation.

Symptoms can appear either in the area where the chemicals were first released or throughout the entire body. Symptoms often appear in the nose, lungs, throat, skin and digestive tract. Common allergy symptoms include:

• Itching of the skin, eyes and nose. Caused by histamine irritation of certain nerve endings.
  
  
• Sneezing, watery eyes and runny nose. Due to the leakage of fluid from the blood vessels.
  
  
• Hives. Caused by swelling and fluid leaking out of local blood vessels.
  
  

  

• Nausea and vomiting.
  
• Wheezing and coughing. Usually involves the inflammation of cells in the breathing areas.
  
• Shortness of breath. Due to the contraction of bronchial tubes.
  
• Diarrhea.

People who think they may be experiencing these symptoms as the result of an allergic cascade should contact an allergist. Allergists can help people identify the substances that trigger their allergic cascades. Once the allergens have been identified, patients can take steps to avoid the triggers and lower the odds of the cascade occurring again.

Since avoidance is not always possible, allergists may also recommend over-the-counter or prescription drugs to prevent or treat the effects of an allergic cascade.

The most severe type of reaction to an allergic cascade is anaphylactic shock. This condition involves breathing difficulties, lowered blood pressure and shock as a result of blood vessel dilation. Anaphylactic shock can be life-threatening and should be treated at the first sign of a reaction. Symptoms of this reaction include:

• Shortness of breath
• Tightness in the chest or throat
• Choking
• Dizziness, lightheadedness or fainting
• Hoarseness
• Severe itching
• Diarrhea
• Vomiting

The earliest effects of an allergic cascade may be experienced within a few minutes of exposure to an allergen. This is known as the early phase of an allergic reaction. This phase of the reaction is marked by the body’s immediate release of chemical mediators upon contact with an allergen to which the body has previously been sensitized. For this reason, this early phase reaction is typically referred to as a hypersensitive reaction. Symptoms at this point can include the full range of allergy responses, including runny nose, itching, tissue inflammation, anaphylactic shock and hives.

In about half of all allergic reactions, the early phase reaction progresses into a late phase reaction, where symptoms appear (or reappear) four to six hours after exposure. Reactions at this point typically include red and swollen inflammations, though the full range of symptoms is often produced, and can include anaphylactic shock. Individuals who are susceptible to this type of reaction are often even more sensitive to subsequent exposures. This type of reaction is commonly associated with chronic allergy symptoms. While late phase allergic reactions usually follow early phase reactions, some late-phase reactions occur without any warning.

The tendency to develop a late phase reaction depends on the type of antigen, patient sensitivity and the concentration of the allergen.