It is estimated that more than 20 percent of the population suffers from hay fever or similar allergies, this doesn't include other types of allergies.
The most often, or should I say commonly discussed allergy at DAN is asthma. Asthma is a chronic lung disease which causes the bronchi (internal breathing tubes of the lungs) to become narrower. The stimuli which can cause this narrowing to occur include exercise, atmospheric irritants and even cold air. Most of these are quite common on a typical dive.
Previous to 1995 diving medicine advised against anyone diving with asthma. However, most recently( after 1995) the Undersea Hyperbolic Medical Society (UHMS) provided guidelines that the required pre-qualifications that asthma sufferers must exhibit in order to dive.
The following pre-qualifications were determined by UHMS:
Two key qualifications for diving candidates with asthma include ensuring that the asthma is of a mild nature and that treatment is working well enough to prevent an acute attack while underwater or on the surface. Following that, it is crucial that anyone with asthma consults with a doctor trained in diving medicine prior to diving.
Read more details here on sportdiver.com
Naturally the range of allergies one may suffer from is rather vast. Some allergies such as allergic reactions to neoprene or rubber, the primary components of wetsuits, can result in varying degrees of discomfort while other types of allergies are far more dangerous when it comes to scuba diving.
If you suffer from any forms of allergies you are advised to seek the advise of a medical doctor before you start/continue diving.
Related articles for reference:
Are You Allergic to Neoprene?
Is diving with severe seasonal allergies ok?
Can I Dive With Asthma?
Wetsuits for those with a neoprene allergy