Understanding medicine is a complex business that requires years of study, often to prove beyond a shadow of a doubt things that sufferers of illnesses have long accepted as fact. One such accepted, though not medically confirmed, fact is that there is a link between asthma and allergies.
While it is known that some substances - such as tobacco smoke - can make asthma more difficult to deal with, there is no conclusive proof of a link between asthma and allergies. Many sufferers believe there is no need to fund expensive medical studies to 'prove' a link that is well known, and is often discussed by doctors during treatment of asthma.
Without medical studies, it is difficult to say what exactly the link is, but it does appear that people who suffer from any severity level of asthma are more likely to suffer from allergies. The most prevalent allergy is to dust mites, or general household dust. While dust has long been known to affect the lungs of asthma sufferers, it would appear that it can also manifest itself as a skin allergy. Sufferers report excessive itching and other physical discomforts aside from problems with their breathing - though these can be controlled using general anti-histamines.
Hay fever is another common affliction that has become associated with asthma, but again this can be dealt with using over-the-counter anti-histamine remedies. It is merely something asthma sufferers should be aware of, as related allergies can apparently appear at any time - no matter how long they have been suffering with asthma. If you find yourself experiencing physical allergy symptoms, contact your GP for diagnosis and treatment.