A Comprehensive Guide to Ten Causes of Shortness of Breath

3. Allergic Reaction

A severe allergic reaction, known as anaphylaxis, can also cause severe shortness of breath. Most people who have an allergic reaction will feel short of breath immediately, although in some cases there can be late-onset symptoms. Anaphylaxis is an emergency situation, so you need to seek medical help right away and administer an epi-pen injection if you carry one. Some people develop allergies later in life, so just because you have never reacted before to food items or bee stings does not mean that you cannot have a reaction in the future.