Asthma is a disease where the smooth muscle in the lungs constricts, leading to the airways becoming inflamed. The muscles constrict in an immune response to a non-toxic stimulus, and sometimes an allergic reaction to numerous environmental stimuli. Asthma attacks are severe cases when the airways constrict so much that the patients lungs swell, causing difficulty breathing and panic. Sometimes, there is a buildup of mucus also, which further reduces the lumen of the airways, making breathing even more difficult. (www.asthma.org.uk)
Prevention and Treatment
Many asthma attacks are preventable, and if specific triggers are avoided then many asthma sufferers can go years without suffering problems. Many of the most common triggers include dust, pets and pollen. Once people learn to avoid their worst triggers then they can control their asthma better. (www.asthma.org.uk)
Asthma can be easily treated using an inhalor. An inhalor is a small device which the patient places in the mouth, pushed to release the contents to allow the patient to inhale the drug into their airways.
Commonly salbutamol and ipatropium are found in reliever inhalors, which are used as a fast acting solution to stop asthma attacks when they happen. These drugs contain brochodilators which, as the name suggests, dilate the bronchi to make breathing easier again. 
Drugs called preventers can be prescibed to reduce the chances of an asthma attack occuring and hence, reduce the need for a reliever inhaler. Preventers contain steroids and can take around two weeks to build up their effect on a person. Once the inhaler has been used continuously and regularly, the person should find that their asthma flare-ups and need for a reliever inhaler reduces significantly. 
What do I do if someone has an asthma attack?
According to www.emedicinehealth.com  approximately 5000 people die in the United States each year from asthma and is one of the most common reasons why people visit A&E and call ambulances. So if somone has an asthma attack it may be life threatening if the situation isnt handled properly and quickly.
As we have developed preventor drugs which drop the rate of asthma attacks to such a low level people often forget to take their inhalors with them when they leave the house, or delay a visit to their GP to get a refill for their inhalor.
If you encounter somone who is having an asthma attack and doesn't have an inhalor, call 999, and explain the situation. Do not use someone elses inhalor, as the drugs contained may be different to what the patient commonly uses (and should the patient be allergic to that drug then the inflammatory response could get worse causing respiratory arrest). Try to calm the patient down and reassure them that they will be fine, but do not ask them to speak a large amount as it will cause more stress to their respiratory system. Wait with the patient until the ambulance arrives.
- ↑ http://www.asthma.org.uk/about-asthma/medicines-treatments/preventer-inhalers/
- ↑ http://www.patient.co.uk/health/inhalers-for-asthma
- ↑ http://www.emedicinehealth.com/asthma/article_em.htm