Cold, flu, COVID, or allergies? A symptom guide

The quick answer: Flu often starts abruptly with fever, aches and exhaustion; a cold is usually milder and more gradual; allergies commonly cause itching and sneezing without fever; and COVID can resemble either a cold or flu. Because symptoms overlap, testing is the most reliable way to confirm COVID and may guide timely treatment.

A scratchy throat in the morning can become a fever by evening—or disappear after allergy medicine. Respiratory symptoms are difficult to identify by feel alone because the same cough, congestion and fatigue can come from several causes.

Clues that point toward each condition

Common cold

Colds usually develop gradually. Runny or stuffy nose, sneezing and sore throat are common. Cough and mild fatigue may follow. Fever and significant body aches are less common in adults.

Influenza

Flu often arrives quickly. Fever or chills, body aches, headache, marked fatigue, cough and sore throat are typical. Not everyone with flu has a fever, especially older or immunocompromised adults.

COVID-19

COVID can cause congestion, sore throat, cough, headache, fatigue, fever, body aches, shortness of breath or digestive symptoms. Loss of taste or smell can occur but is not present in every case. Symptoms alone cannot reliably distinguish COVID from flu or a cold.

Seasonal allergies

Itchy or watery eyes, an itchy nose or inner ear, repeated sneezing and clear nasal drainage favor allergies. Fever and body aches are not typical. Allergy symptoms may continue for weeks and track with pollen, pets, dust or another exposure.

At-a-glance symptom clues

When should you test?

Test for COVID when you have compatible symptoms or a recent exposure, especially if you are at higher risk for severe illness or will be around someone vulnerable. A negative home test early in illness may not be definitive; follow current test instructions and clinical guidance.

Flu testing may be useful when the result will change treatment or infection-control decisions. A clinician can often make a treatment decision based on symptoms, timing and local flu activity.

Why early care can matter

Prescription antivirals for flu work best when started within the first one to two days, although treatment may still help later for people who are severely ill or at higher risk. COVID treatments for eligible higher-risk patients also must begin within a limited number of days after symptoms start. Do not delay asking for care while trying to identify the illness perfectly at home.

How Hoag On-Demand can help

Hoag On-Demand provides 24/7 virtual urgent care for cough, fever, flu-like symptoms, sore throat and COVID concerns. A Nurse Practitioner can assess symptom timing and risk factors, discuss testing and treatment options and help determine whether you need in-person evaluation or follow-up.

Seek emergency care for difficulty breathing, persistent chest or abdominal pressure, confusion, inability to stay awake, seizure, severe weakness, blue or gray lips, signs of severe dehydration, or fever or cough that improves and then returns worse.

Frequently asked questions

Can you tell the flu from COVID by symptoms alone?

Usually not with confidence. The symptoms overlap significantly, and testing may be needed.

Do allergies cause fever?

Seasonal allergies do not typically cause fever. Fever suggests an infection or another condition.

When should I ask about flu medicine?

As early as possible—ideally within the first 48 hours—especially if symptoms are severe or you are pregnant, older or have a condition that raises complication risk.

Can Hoag On-Demand evaluate a child with cold or flu symptoms?

Hoag On-Demand serves California residents ages 12 to 17 when a parent or legal guardian is present, and adults 18 and older. Younger children need another care option.