Allergic diseases refer to a range of conditions that occur when the immune system reacts abnormally to otherwise harmless substances known as allergens. These conditions arise due to an overactive immune response to allergens, resulting in various symptoms and allergic reactions. Some common allergic diseases include:

1. Allergic Rhinitis: Also known as hay fever, allergic rhinitis is an allergic response characterized by symptoms such as sneezing, itching of the nose and throat, congestion, and nasal discharge. It is often triggered by outdoor or indoor allergens like pollen, dust mites, or pet dander.
2. Asthma: Asthma is a chronic respiratory condition in which the airways become inflamed and narrow, leading to difficulty breathing, wheezing, coughing, and chest tightness. Allergic asthma is triggered by specific allergens, leading to an immune response and subsequent airway inflammation.
3. Allergic Conjunctivitis: Allergic conjunctivitis affects the eyes, causing itchiness, redness, watering, and swelling of the conjunctiva (thin tissue covering the front of the eye). It can be triggered by allergens such as pollen, pet dander, or certain irritants.
4. Atopic Dermatitis: Atopic dermatitis, also known as eczema, is a chronic inflammatory skin condition characterized by dry, itchy, and red patches of skin. It is often associated with a family history of allergies and can be triggered by allergens, irritants, stress, or changes in temperature or humidity.
5. Food Allergies: Food allergies occur when the immune system reacts to certain proteins in food. Common food allergens include peanuts, tree nuts, cow’s milk, eggs, wheat, soy, fish, and shellfish. This allergic response can range from mild symptoms like hives to severe, life-threatening reactions called anaphylaxis.

Features of allergic diseases include:

• Immediate reaction: Allergic diseases often trigger an immediate hypersensitivity reaction upon exposure to the allergen. This can involve the release of inflammatory substances like histamine, resulting in symptoms that can manifest within minutes or a few hours after exposure.
• Systemic involvement: Allergic diseases can affect various body systems. For example, allergic rhinitis primarily affects the respiratory system, while atopic dermatitis affects the skin. However, some allergies, like food allergies or anaphylaxis, can have systemic effects on multiple organs.
• Sensitization: Allergic diseases usually develop after repeated exposure and sensitization to specific allergens. Initially, the immune system recognizes the allergen as harmless, but repeated exposure can lead to the development of allergic responses.
• Triggers and symptoms: Allergic diseases have specific triggers that cause symptoms upon exposure. Symptoms can vary depending on the type of allergy but commonly include itching, inflammation, sneezing, nasal congestion, hives, difficulty breathing, or gastrointestinal disturbances.
• Chronic nature: Most allergic diseases persist over time, with symptoms recurring upon exposure to allergens. It often requires long-term management and avoidance of triggers to control symptoms effectively.

If you suspect you have an allergic disease or experience any related symptoms, it is advisable to consult with a healthcare professional or allergist who can provide an accurate diagnosis and guide you on appropriate management strategies.