Getting to know

The speed of onset of symptoms of anaphylaxis is very variable and it is not possible to make a general rule regarding the speed of onset of symptoms in anaphylaxis because it depends of several factors such as:

• The quantity and concentration of the allergen that was ingested or injected (the highest the quantity the faster the onset)
• How sensitive the person is to the allergen: in very sensitive people contact with traces of the allergen can trigger an anaphylactic attack. For example people very sensitive to fish or peanuts can develop an anaphylactic reaction from vapours resulting from cooking of these foods. Also, some cases have been reported where very sensitive people developed anaphylaxis when kissing another person who has eaten a food to which they are allergic.
• The means of coming into contact with the allergen: usually anaphylaxis to injected allergens (ex. drugs and insect venoms) tends to have a faster onset – frequently within minutes up to a half an hour - than attacks caused by ingested allergens (foods and orally administered drugs) in which the symptoms can be delayed for up to two hours. However, food reactions can often begin within minutes after the trigger food is consumed.

After occurrence of the first symptoms, progression of anaphylaxis is usually very fast, most symptoms developing in the following 10-20 minutes. 

Very often if the anaphylactic reaction was not very severe the symptoms can disappear spontaneously in a matter of minutes of hours. However, in severe cases epinephrine is always required as an immediate treatment save your life. Complete resolution of symptoms both in mild or severe cases of anaphylaxis requires additional treatment in the emergency room.

In most patients the anaphylactic attack is resolved once the appropriate treatment is applied (epinephrine + additional measures in the emergency room). However, in a number of cases, a second anaphylactic attack, not related to a new exposure to the eliciting allergen, can occur after several hours during which the person is complete asymptomatic. This is known as biphasic anaphylactic reaction. Even though these are rare cases, you should remain alert and record any symptoms that might suggest a new attack for up to 24 hours from the initial attack. Also you have to make sure that you have available a loaded epinephrine pen and the emergency kit in case that you will need them again. (The treatment of the second attack is identical with the first one - epinephrine injection as soon as gravity signs are present and referral to the emergency services).