About one in three people have allergies in the U.S., including children, but many people are underdiagnosed or undiagnosed. Only about 10 to 20 percent of the population knows they have allergies, with the majority being unaware of what they’re allergic to.

Allergies occur when your immune system mistakenly identifies a harmless airborne substance as harmful. Your immune system then produces antibodies – which are substances that normally protect your body from things that make you sick – to this harmless substance. The next time you come in contact with it, these antibodies recognize it and signal your immune system to release chemicals, like histamine, into your bloodstream. These immune system chemicals cause a reaction that leads to the symptoms of hay fever.

Hay fever, also referred to as allergic rhinitis, is caused by an allergic response to outdoor or indoor allergens, like pollen, dust mites or pet dander. Hay fever causes cold-like symptoms, such as runny nose, itchy eyes, congestion, sneezing and sinus pressure. But unlike a cold, hay fever isn’t caused by a virus.

It’s often hard to distinguish the difference between allergies and the common cold. Allergies are characterized by histamine. Histamine is released in and around the nose and is associated with itch. When someone has itchy eyes, nose and throat, plus sneezing that lasts for a few days, it’s most likely allergies. With a cold, you’ll typically experience congestion, mucus, coughing and much less sneezing.

There are common allergy triggers that can cause a reaction year-round, but many people also suffer from seasonal triggers. In spring, tree pollen is a common trigger. Grass pollen triggers allergies starting in early summer; rag weed pollen triggers allergies starting in August and molds affect allergies more during winter.

Because California has very mild seasons, you may see a swing in all of those triggers depending on the humidity, significant weather changes or long periods of drought. Many of the common seasonal allergy triggers don’t apply in Southern California.

A common misperception is that if someone takes an over-the-counter antihistamine and feels better, they must have allergies. Antihistamines are a good drying agent, but because someone responds to an antihistamine doesn’t mean they have allergies.

For this reason, it’s important to have an allergist determine what you’re allergic to. There are two types of tests used to determine allergies. During a skin test, small amounts of material that can trigger allergies are pricked into the skin. If allergic, the patient will develop a raised bump.

A blood test can also measure the immune system’s response to a specific allergen. A blood sample is sent to a laboratory, where it can be tested for evidence of sensitivity to possible allergens.

After you’ve been tested, the next step is determining what type of treatments will work best for you. Your allergist may recommend tips to reduce common triggers in your home or they may recommend using medication.

Allergies can be overwhelming for many people, but they don’t need to be. With the proper testing, preventative care and treatment, people with allergies can live happy healthy lives.