Hypersensitivity (Hypersensitivity Vasculitis)

Hypersensitivity is a general term for an extreme allergic reaction to a drug or substance. The most common type of hypersensitivity, or type 1, is usually marked by a red or purple-ish rash and/or hives.

There are four types of hypersensitivity: Immediate, antibody-dependent, immune complex disease, and delayed-type.

Here's more on the characteristics of hypersensitivity, causes and examples of hypersensitivity, the types of hypersensitivity, and treatment.

Symptoms of Hypersensitivity

Symptoms of hypersensitivity include:

• A rash that includes purple or brown spots
• Sores on the lower body
• Blisters, hives, or open sores or ulcers
• Hay fever

Type 1 hypersensitivity can cause anaphylaxis, which is an extreme allergic reaction that can be deadly. Symptoms of anaphylaxis include:

• Abnormal breathing
• Swollen tongue or swelling in the throat
• Difficulty talking
• Wheezing or coughing
• Stomachache
• Vomiting
• Dizziness
• Fainting

Causes of Hypersensitivity

Hypersensitivity is caused by an extreme immune reaction to a foreign substance or illness. The most common type of hypersensitivity, or type 1, can be caused by everyday interactions with substances like pollen or pet hair. Other types of hypersensitivity can result from medications and chronic medical conditions.

The Four Types of Hypersensitivity

The four types of hypersensitivity are:

Immediate Hypersensitivity (Type 1)

Type 1 hypersensitivity, the most common type, is an immediate allergic reaction ranging from mild to severe. It occurs when the body releases proteins that fight against foreign substances (antibodies) in response to a substance the body is allergic (allergen).

Common allergens that can cause type 1 reactions include:

• Pet hair
• Mold
• Pollen
• Dust mites

Antibody-Dependent Hypersensitivity (Type 2)

Type 2 hypersensitivity can take two to 24 hours to appear and is marked by antibodies that can destroy cells and cause tissue damage. Type 2 hypersensitivity reactions can occur during or because of:

• Blood transfusion reactions
• Reactions to organ transplants
  
• Drug reactions
• Neuromuscular disorders
• Autoimmune diseases

Type 2 hypersensitivity can take days to weeks to develop. It is marked by antibodies that combine with proteins and then set into the body's tissues, which results in inflammation (the body's response to foreign invaders).

Immune Complex Disease Hypersensitivity (Type 3)

Type 3 reactions can be a part of inflammation associated with:

• Arthritis
• Lupus
• Serum sickness (a reaction to medications like drugs that prevent organ transplant rejections)

Delayed Type Hypersensitivity (Type 4)

Type 4 hypersensitivity, the second most common type, takes at least two days to develop and is marked by skin redness. Examples include:

• Poison ivy
• Contact dermatitis
• Reactions to diagnostic skin tests

Hypersensitivity Treatment

Treatment of hypersensitivity reactions can depend on type. The most common methods are:

Type 1 treatments include:

• Antihistamines
• Anti-inflammatories
• Bronchodilators: Medications that help lung function.
• Epinephrine: Epinephrine treats anaphylaxis,

Type 2 treatments include:

• Avoiding triggering substances or drugs
• Discontinuing medications that cause reactions
• Glucocorticoids (steroids)
• Immunosuppressant therapy: These are medications that suppress the immune system to prevent reactions.

Type 3 treatments include:

• Avoiding substances that trigger an allergic response
• Glucocorticoids (steroids)
• Antihistamines
• Drugs to manage autoimmune disorders

Type 4 treatments include:

• Removal of the offending agent
• Corticosteroids
• Fluid therapy in a hospital (in extreme cases)
• Methotrexate

Summary

Hypersensitivity refers to extreme allergic reactions to substances and drugs. The most common type of hypersensitivity, or type 1 (immediate), includes sudden allergic reactions that cause hives or rashes. Treatments for hypersensitivity can range from antihistamines and steroids for inflammation to antibiotics and epinephrine.