A noninfectious unnatural and unusual reaction to a substance or condition is

The correct option is A Allergy
Allergies, also known as allergic diseases are a number of conditions caused by hypersensitivity of the immune system to typically harmless substances (non-infectious) in the environment. Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling. Hence, Allergy is a noninfectious, unnatural and unusual reaction to a substance or condition.

So, the correct answer is 'Allergy'.