What are the signs of an allergic reaction to the dentist's numbing medicine?

Not typical: An adverse reaction to dental anesthetics is rarely a true allergy but rather a psychogenic or epinepherine reaction, which is typically a racing heart, palpitations, sweating, nervousness or feeling faint. If a true allergic reaction were to happen, it would be most likely in the form of anaphalaxis.

Inflammation: Allergic reactions to local anesthetics are very rare, but possible. Depending on the type of hypersensitivity reaction, (allergy is typically termed hypersensitivity type I, or immediate) you can have different symptoms. Commonly you might experience nausea, trouble breathing, hives, itchy skin, cough, runny nose, or swelling. If you have trouble breathing, seek immediate medical attention.

LA allergy: Two distinct types of allergic reactions to local anesthetics: 1-Allergic contact dermatitis and delayed swelling at the site of administration; 2-Urticaria and anaphylaxis – These types of reaction are RARE. I have personally never seen or heard of one at dentist's office in over 40 years. Poor injection technique or sensitivity to Epinephrine in anesthetic can cause racing heart, sweating, etc.