Allergy is highly un-predictable disease and it can happen to anyone in this world even anytime. It is a universal disease not controlled by age, money or sex. Speaking scientifically it is a refusal reaction of body for any unwanted and harmful foreign object. The reaction can be in form of vomiting, sneezing or rashes on skin. Unfortunately for each person it is different and need to be treated different each time it is encountered. The sole reason for this is the difference in physiology of any two persons in the world. No two persons have same biological signature in this world and this is science proven thing.
Allergy commonly occurs as simple reaction only like skin rash, but in few cases it can be life threatening. A known serious reaction of allergy is blood refusal in a blood transfusion process, few times body don’t accept the foreign blood and therefore develops life threatening allergy. A simple and common allergy is cough allergy.
Allergy can be of any type water, air or food also. In current generation we have thousands of different kinds of allergies exists but it’s impossible for today’s science to know which might come in our way. Fortunately we have an allergy test but unfortunately it is kind of limited in nature. The only way right now to know about many allergies is when you encounter with that object in real world. The Common allergy symptoms include rashes on skin, dizziness, vomiting, blur in vision etc; it is wise decision that you consult a doctor when you encounter a new object and develop some allergic reaction to it.
Chocolate allergy is an interesting and weird allergy I have seen; in reality it is actually allergy to some ingredient of chocolate, not to the Chocó. So next time you eat chocolate check that you dont have allergy to any ingredient.