Please note: Information in this post is not meant as a substitute for veterinary care. Always consult your veterinarian in an emergency.
You should call your vet immediately if there is an allergic reaction. They should be treated as soon as possible.
If the allergic reaction is mild, call your vet and you might give Benadryl to help your dog. Most vets recommend 1 mg per pound. Those mild allergies are usually skin irritations. Urticarial is rapid swelling and redness of the lips, around the eyes, and in the neck region and can be very itchy. You should still see a vet to prevent your dog from going into anaphylaxis.
Allergic reactions can result from a variety of causes including insect bites or stings, food reactions, environmental issues, and vaccines. If your pet has a history of allergic reactions, talk to your vet about proper preventative options for your dog.