What are the differences between a cold and allergies?

Big differences: Colds are due to viruses and are contagious but limited to less than a week. Allergies typically have itching (nose, eye) and sneezing as common symptoms. Symptoms can continue through a pollen season or for months or years (if indoor allergies). Allergies response well to treatment with medications and allergy injections. An allergist can assist in identifying if there is an allergy.