What is allergy?Allergies happen when the body’s immune system reacts to irritants such as pollen and house dust mites that are otherwise harmless. For most people these tiny particles are insignificant, but for people with allergy, they can trigger an allergic reaction such as shortness of breath, itchy and watery eyes, blocked and runny nose, sneezing and asthma.
Any substance that causes the body’s immune system to react in this way is called an allergen. Common allergens are:
• House dust mites• Pollens• Animal dander (hair, skin)• Fungal or mould spores• Food (particularly milk, eggs, wheat, soya, seafood, fruit and nuts)• Wasp and bee venom• Some medicines• Latex• Household chemicals (irritants such as detergents and fragrances)
What are house dust mites? Dust mites are tiny bugs that are too small to see. They live off human skin flakes and are found in many homes in mattresses, bedding, carpets, soft furnishings, clothing and fabric-covered items. Dust mites thrive in warm and humid environments, which is why they prefer to live in beds with lots of moisture from our breath and bodies, and shed skin cells. Unlike pollen, house dust mites are present all year round, causing constant allergy symptoms.
It’s not the dust mites itself that cause symptoms but proteins in their droppings or body parts, even after the dust mite has died. When these proteins are inhaled or touch the skin, the body produces antibodies that cause swelling and irritation. If inhaled it causes irritation of the upper and lower respiratory airways.
Types of allergyThere are several types of allergies:
• Respiratory allergy: Respiratory allergies are the most common allergies. Respiratory allergies are caused by allergens in the air and general environment, including pollens, animal dander, moulds and house dust mites. The most common forms of respiratory allergies are allergic rhinitis and allergic asthma.
Allergic rhinitis, commonly known as hay fever, is inflammation and irritation of the upper airways and the membranes of the nose and eyes. Conjunctivitis often accompanies this condition. Symptoms of allergic conjunctivitis are red, watery and itchy eyes. The most common cause is an allergy to grass and tree pollen.
Allergic asthma is when the airways are hypersensitive to the allergens causing an allergic reaction in your body. Since the upper and lower airways are connected, inflammation can spread from the nose into the lungs and worsen asthma control or lay the foundation for later asthma development.
• Skin-related allergy: Eczema, also called contact allergy or contact dermatitis, is an overreaction in the skin caused by direct contact with nickel, cosmetics and chemicals, among others.
• Other allergies: Other allergies include food allergies, most often caused by milk, eggs, soy, peanuts and fish, and allergy to insect venom. Symptoms typically show shortly after coming in contact with the food or being stung by an insect. Common symptoms include rashes, wheezing, itching, an upset stomach, nausea and vomiting. In rare cases, a food or insect venom allergy can lead to anaphylactic shock, which is a severe, sometimes fatal, whole-body allergic reaction.
Who is at risk?It’s currently estimated that approximately 10-30% of the world’s adult population and up to 40% of children are affected by some form of allergy. Allergic rhinitis (with or without conjunctivitis) affects 5-50% of the population worldwide, and 15-20% of these suffer from a severe form of allergy.
Important factsAllergies are the most frequent chronic diseases in children and young adults.
Allergies run in families, but most new cases appear in people without a previous family history of allergy.
Allergies can develop at any age, but they usually start in childhood and persist for many years, often for life. Some people are more likely to develop allergy because it runs in their family. The genetic tendency to develop allergies is known as atopy. If a child has one parent with allergies, there is a 30% risk that the child will develop allergic rhinitis. The risk increases to 70% if both parents have allergies.
Causes of allergyThough the exact role is unknown, environmental factors may play a part in the development of allergy. Several factors seem to increase the risk of a child developing atopy, such as growing up in a house with smokers, using antibiotics, and exposure to pets and house dust mites. However, high or low exposure may also result in the development of tolerance to house dust mites and pets among children.
Children with one form of allergy can often go on to develop other forms of allergy during their childhood. For instance, children with food allergies at a very young age may develop respiratory allergies as they grow older. This progression of allergic diseases is known as ‘the allergic march’. The word ‘march’ suggests that children pass through from one stage of allergy to another.
There is a strong correlation between allergic disease in the upper and lower airways. The majority of people with house dust mite respiratory allergic disease have allergic rhinitis, and about half of people suffering from house dust mite allergic rhinitis suffer from allergic asthma.
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