Most of us breathe too deeply.
Breathing is normal when you have proper balance between production and elimination of carbon dioxide. If you breathe more than you need you are loosing carbon dioxide and won't have sufficient in your body. This type of breathing is called hyperventilation.
If you breathe properly carbon dioxide in your lungs is at 6.5% because that is the ideal ratio for you.
Chronic Hyperventilation Syndrome (CHVS) has been studied and documented in the medical literature for a long time. Many authoritative reports have been written on it. But although it is very common condition, it is frequently ignored by mainstream western medicine.
If you have asthma and go to your doctor you are more likely to get prescription drugs which can in themselves be harmful to your health, rather than help learning to get rid of it for life by breathing properly.
Buteyko therapy is named after Ukrainian medical doctor and research scientist, Professor Konstantin Buteyko. He developed what is now called Buteyko breathing to reverse Chronic Hyperventilation Disorders.
Professor Buteyko's realized that many diseases like asthma are caused by breathing too much.
The best way to learn Buteyko breathing would be to find a Buteyko teacher close to you and attend classes. Here is a description of what is entailed:members.westnet.com.au/pkolb/but_strt.htm