A sniffle here, a cough there and suddenly a cold has come. What to do? Here’s how to treat — and not treat — a cold.

QUESTION: How do you know if you have a cold?

ANSWER: The “common cold” lasts three to 10 days, though a cough can stick around longer, said Dr. Donna Meltzer, residency director in the Department of Family Medicine at Stony Brook University in New York.

“It is characterized by variable degrees of sore throat, sneezing, nasal congestion and runny nose, low-grade fever, generalized malaise and sometimes headache,” she said. “There are many types of viruses that cause colds, and infection is spread through the air when someone coughs or sneezes, or by direct contact with an infected person shaking hands or a contaminated surface like a doorknob.”

QUESTION: Are there effective home remedies?

ANSWER: Doctors still recommend the age-old standbys: Get rest and drink a lot of fluids, which help thin the mucus.

Gargling with salt water is also a good idea, said Meltzer, who recommends mixing ¼ teaspoon of salt in 8 ounces of water. Though studies differ on whether it’s effective, she said that, in her experience, it temporarily relieves the pain of a sore throat. It might even be helpful to gargle every day when you aren’t sick. “Some newer studies suggest that individuals who gargle three times daily with water have fewer cold symptoms,” she said.

QUESTION: What are the best options at the drugstore?

ANSWER: A pharmacist can help people with colds choose the best over-the-counter medication. But, it’s important to tell the pharmacist about any conditions such as diabetes, heart problems, high blood pressure or glaucoma because cold medications can exacerbate them, said Mark Macchia, associate director of pharmaceutical services at Mercy Medical Center in New York.

Also note other medications that you’re taking, keeping in mind that your pharmacist may not have a complete picture of your medical history, he said.

QUESTION: What about decongestants and antihistamines?

ANSWER: “In adults, over-the-counter decongestants taken by mouth like Sudafed and nasal sprays like Neo-Synephrine might temporarily provide relief of nasal stuffiness,” Meltzer said. “Studies indicate that antihistamines such as Benadryl are ineffective alone, but might relieve some nasal symptoms when combined with a decongestant. Some feel that guaifenesin for cough might help.” Prescription nasal sprays may also provide relief, she said.

Macchia noted that it’s important to follow the instructions about how long you should use medicated nasal sprays, which can be effective in the short term but cause problems if taken over more than a few days.

Saline nasal sprays, which moisten the nasal passages, can be used indefinitely, but medicated sprays can cause what’s called a rebound effect, actually making congestion worse if they’re used too long, he said. His recommendation for someone who wants to use a nasal spray is a 12-hour spray.

QUESTION: Do you treat a child with a cold the same as an adult?

ANSWER: Avoid giving aspirin to kids because it can cause serious side effects. “In both children and adults, acetaminophen and nonsteroidal anti-inflammatory drugs such as ibuprofen are helpful in reducing a fever and relieving headache and body aches,” Meltzer said.

Also keep in mind that cough and cold medications are usually not advised in children younger than 6 years and should not be used in children younger than 2, she added.

QUESTION: How active, or inactive, should you be with a cold?

ANSWER: “If you have a fever, you should probably stay home from school and work,” Meltzer said. “I also do not allow athletes to exercise or compete in sports if they have a fever.”

The picture changes, though, once all that’s left of your cold are what she called “residual cold symptoms” -— slight cough or runny nose without fever. For the average person whose cold has progressed to that point and who feels well, she said, going to work or school is probably OK.