During cold and allergy season, people develop symptoms consistent with colds and allergies, including runny noses, stuffiness and sneezing. If the nasal secretions are not kept under control, they begin dripping down the back of the sufferer’s throat, causing discomfort . . . and asthma attacks.
Post-Nasal Drip Triggers Asthma
Among other commonly known asthma triggers, post-nasal drip (PND) is on the list. Asthma and post-nasal drip are connected to each other because of the irritating effects of post-nasal drip on your throat and lungs, says the University of Iowa Hospitals and Clinics. If you have a chronic condition that causes PND, along with asthma, you’re more likely to experience the “double whammy” effect of that irritating “drip-drip-drip” sliding down the back of your throat and leading to the chest tightness and closed-throat feeling you get from an asthma attack. 
In addition to asthma exacerbations, your post-nasal drip may cause you to develop a chronic cough or sore throat. The secretions don’t have to be thin to cause irritation. Post-nasal drip can develop from excessive or thick nasal secretions, according to MedicineNet. 
Description of PND
Post-nasal drip is an accumulation of mucus that develops in the back of your nose and throat. This accumulation causes you to feel as if you have mucus dripping down the back of your throat, down from your nose.
Mucus, itself, serves a health purpose in your body. Normally, you produce about two quarts of mucus daily. This keeps your respiratory tract moist and clean – usually. Cilia (tiny, microscopic hairs) line the inside of your nasal cavities, helping to move away particles like dirt. This mucus eventually moves to the back of your throat, where you swallow it.  When you have allergies, your body’s production of mucus goes into overdrive. You begin sniffling, wiping your nose with facial tissue, sneezing and blowing your nose. If your body’s overproduction of mucus is sufficiently high, you may develop an upset stomach from the accumulation of mucus in your stomach.
Connection Between PND, Allergic Rhinitis and Asthma
If you have asthma and post-nasal drip, you may be more likely to suffer from allergic rhinitis, which is an inflammation of the inner lining of your nose. You may have a runny nose, sneezing, nasal congestion and itching. Those with allergic rhinitis are more likely to suffer from eczema and asthma.
Seasonal allergic rhinitis develops when pollen in the air irritates your system. This form of rhinitis usually happens at specific times of the year. Perennial allergic rhinitis is usually present year-round and is caused by animal dander and dust.
Regardless of the type of rhinitis you suffer from, the overproduction of mucus in your nasal cavities leads to PND. The PND triggers asthma attacks. 
 Asthma Triggers. University of Iowa Hospitals & Clinics, retrieved at https://www.uihealthcare.com/depts/asthma/AboutAsthma/triggers.html
 Chronic Rhinitis and Post-Nasal Drip. MedicineNet.com, retrieved at https://www.medicinenet.com/chronic_rhinitis/article.htm