As fall settles in across the U.S., millions of Americans may find themselves battling seasonal allergies, colds or the flu — illnesses with overlapping symptoms that can be difficult to tell apart.

As the season brings chilly temperatures, many people get sick because of the sudden shift from pleasant warmth to cold; this works alongside fall allergies, often worsening both symptoms.

Colds, flu and allergies all affect the respiratory system, making it hard to breathe, especially when multiple illnesses combine.

Fall allergies are often triggered by pollen or mold in the air and are not caused by viruses, unlike the cold or flu.

When suffering from allergens, the body’s immune system reacts to a trigger or allergen, which is something you are allergic to.

“If you have allergies and breathe in things like pollen or pet dander, the immune cells in your nose and airways may overreact to these harmless substances,” Dr. Teresa Hauguel, News in Health expert, said on infectious diseases that affect breathing.

Common fall allergy symptoms

• Sneezing
• Runny or stuffy nose
• Itchy or watery eyes
• Itchy nose or throat
• Postnasal drip
• Mild cough

Each condition has key symptoms that set it apart from allergies.

Distinguishing a common cold from fall allergies can be difficult, but these symptoms set them apart. Both a cold and the flu can cause a runny, stuffy nose, congestion, cough and sore throat that can last for days.

If you have fall allergies, the best way to treat yourself is to limit outdoor exposure, where pollen and other triggers can have an effect.

Millions of Americans are in a battle as autumn has settled in over how to tell the difference between whether they have allergies during the fall or are suffering from a cold. Getty Images

Over-the-counter antihistamines and nasal spray can provide quick relief if the symptoms are too unbearable.

Colds are caused by a virus, which is often caught through engaging with contaminated surfaces or respiratory activity, according to Southern New Hampshire Health.

When an infected person talks, coughs, sneezes or even breathes, they release virus-filled droplets into the air. If you are within 3 to 6 feet of the infected person, you become susceptible to these droplets landing in your mouth, nose and eyes.

Allergies trigger itchy eyes, while viral colds cause sore throats, body aches, and mild tiredness. AFP via Getty Images

Common cold symptoms

• Runny or stuffy nose
• Sneezing
• Sore throat
• Cough
• Mild tiredness
• Mild body aches

Most people with cold or flu-like symptoms recover on their own without medical care, but it is always worth checking in with a healthcare provider if symptoms persist beyond 10 days and over-the-counter medicines don’t work.

To treat a cold or flu, experts suggest getting plenty of rest and drinking lots of fluids.

The more severe these symptoms are, the larger the indication that you are suffering from an illness and not common fall allergies.

Cold treatment options

• Nasal congestion — Pseudoephedrine or topical intranasal oxymetazoline (limit topical decongestants to no more than three days to avoid rebound rhinitis).
• Cough — Dextromethorphan or honey.
• Fever/aches — Acetaminophen or NSAIDs (Ibuprofen is more effective than acetaminophen for fever-related discomfort).

A fever is rarely associated with a cold and often indicates a more serious illness, like the flu.

If you have second thoughts that you’re suffering from the flu and not a cold, a good rule of thumb is that flu symptoms are typically much more severe when compared to a cold.