NEW YORK (CBSNewYork) – A warning Thursday for the many people using over-the-counter nasal sprays: One type has to be used very carefully.

It can actually make your nasal stuffiness worse and create serious problems, including addiction.

We’re in prime allergy season, so millions of people are using nasal sprays to relieve stuffiness.

They are very effective and safe when used as directed, and that’s the key, because they can have some surprising side effects.

Whether it’s all the pollen in the air during spring allergy season, or just a plain old head cold, nasal congestion is one of the most common complaints people have all year round.

“Especially in allergy season, I have chronic congestion,” said Shanna Cohen.

Like millions of others, Cohen turns to nasal sprays for relief. But she has learned the hard way which to use and how to use them safely.

Plain saline sprays are good for moisture and to flush pollen out of the nose, but they won’t do much for stuffiness. That’s where decongestant sprays are very effective.

“There are over the counter sprays that shrink the blood vessels in your nose and give relief, but they squeeze and have side effects,” said Dr. Clifford Bassett of Ashtma & Allergy Care of New York. “That can cause rebound congestion, where the stuffiness, where the problem is worse than it was in the first place.”

The problem is that the mucus membranes of the nose are swollen and inflamed, whether from pollen or viruses, CBS2’s Max Gomez reported.

Decongestant sprays shrink the the blood vessels in those membranes, reducing the swelling and allowing you to breather. But eventually, those tiny blood vessels stop responding to the sprays. That’s called rebound congestion.

“I’ve had some bad rebound congestion for a couple of days where nothing does the trick,” Cohen said.

That leads to using more of the spray, less effect, and more overuse – nasal spray addiction and possible side effects, Gomez reported.

“People who overuse for long time, nasal perforations, nose bleeds are complications of the drying effect of using nasal decongestants more than indicated, weeks and longer,” said Basett.

The sprays that are safe are nasal steroids. They are anti-inflammatory and shrink the mucus membranes without drying or rebound effect.

Those steroid sprays can take a few days to take effect. That’s why people turn to the decongestants for immediate relief.

To be clear: The decongestants are safe and effective when used correctly. Just read the labels.

If you need them for days or weeks, see a doctor for an alternative.