The term ‘allergens’ refers to biological particles that cause an allergic responses in some people. According to the NHS, allergies affect more than 1 in 4 people in the UK at some point in their lives. In a 2011 report, charity ALLERGY UK estimated that at least 12 million people in the UK were allergic to their own home (or something in their homes). The most common allergens in the host are dust, excrement from dust mites (tiny creatures, about a quarter of a millimetre long, which live off human skin scales, and are normally found in bedding, carpets, soft furnishings), MOULD spores, pet dander (very tiny particles of skin that have been shed from animals with fur or feather), and pollen (released from grass, trees, and weeds during the early spring and summer months and can migration indoors). Allergens are sensitisers and can trigger rhinitis (inflammation of the inside of the nose) and exacerbate other respiratory illnesses such as asthma. Allergen levels are elevated in humid and damp conditions.