Seasonal allergies (allergic rhinitis, hay fever) occur when your immune system has an overactive response to a type of substance called an allergen. Common seasonal allergens include tree pollen, grass pollen, mold, and ragweed (which releases pollen). Pollen is a tiny powder that flowering vegetation like plants, trees, weeds, and grass release as part of their reproductive process. Mold is a fungus that releases tiny spores into the air.

Most plants release pollen in warmer seasons, such as the spring and summer. Ragweed pollen and mold are highest in the late summer and fall.

Seasonal allergies affect 60 million people per year in the United States. About 25% of adults and 19% of children have at least one seasonal allergy. Common symptoms include sneezing, watery eyes, and a runny nose. The most common treatments are antihistamines and nasal (nose) corticosteroids. Those with severe allergies may require allergy testing and advanced treatment.

Seasonal allergy symptoms can range from mild (don't disrupt daily life) to severe (disrupt multiple daily activities or sleep). The following are characteristic symptoms.

When your immune system identifies generally harmless substances, like pollen or mold, as a threat, it releases chemicals called histamines in defense. While the histamines are trying to help your body "fight" the threat, they are causing the inflammation that leads to allergy symptoms.

Allergy season starts for many people in the spring when trees like oak, birch, cedar, and maple release pollen. For others, it begins in late spring or summer as grass pollinates. Mold allergies are more common during rainy seasons but can grow in humid indoor conditions. Fall seasonal allergies are typically due to:

Ragweed is the most common allergen in the U.S. It blooms and pollinates from August to November, but levels are highest in September.

Those with a family history of allergies or asthma are at a greater risk of experiencing seasonal allergies. Many people also have other allergy triggers, such as:

The following factors can influence the severity of allergy symptoms:

If you have seasonal allergy symptoms, your healthcare provider will review your medical history and do a physical exam. The following are additional clues that may cause them to suspect that you have seasonal allergies:

Your provider may refer you to an allergist -- a medical doctor who specializes in allergic conditions such as allergies and asthma.

Your allergist may recommend the following diagnostic tests in severe cases, especially for those who do not respond to treatment:

Imaging tests like X-rays or computed tomography (CT) scans may also be recommended to rule out other conditions like sinus infections, nasal polyps (non-cancerous growths in the nose), or deviated septum (crooked divider in the nose).

Though there is no cure for seasonal allergies, the following treatments can help manage and alleviate symptoms.

Intranasal corticosteroids are nose sprays that work by calming down the immune response. This reduces swelling and irritation in the nasal passages. They are usually the first line of treatment, and examples include:

Antihistamines block the histamine your body generates, reducing inflammation (swelling). Benadryl (diphenhydramine) works best for sudden or current allergy symptoms. But it can make you drowsy. Other common preventive antihistamine medications include:

Decongestants reduce inflammation in the nasal passages, but it's important to only use them for a few days to avoid unwelcome side effects and rebound congestion. Examples of oral decongestants are Sudafed PE (phenylephrine) and Silfedrine, Sudafed (pseudoephedrine). Intranasal decongestants include Afrin, Neo-synephrine, Vicks Sinex (xylometazoline), or Astepro (azelastine).

For itching, watery, or swollen eyes, you can try putting a cool cloth over them for a few minutes. You can also try over-the-counter or prescription eye drops. Types of eye drops include:

Leukotriene receptor antagonists like Singulair (montelukast) are other oral medications that your allergist may suggest. However, studies show they are less effective for seasonal allergies than nasal corticosteroids.

Cromolyn (sodium cromoglycate) is a mast cell stabilizer. This preventive medication stops the release of histamines. It comes as an oral solution, inhaler, or eye drops. Allergists commonly prescribe it to prevent allergies in people with asthma.

Immunotherapy is when your allergist gives you minimal doses of an allergen over increase over time to slowly desensitize your body. Some are subcutaneous (under the skin) shots, and others are sublingual (under the tongue). This is a long-term treatment for those with severe allergies who don't respond to medications.

Xolair (omalizumab) is a subcutaneous injection that prevents immunoglobulin E (IgE) -- a type of antibody that your immune system creates -- from triggering allergy symptoms. Providers typically reserve it for people with allergic asthma, hives, or nasal polyps that other medications have not been able to control.

While you can't avoid exposure to allergens altogether, you can take the following steps to reduce your exposure:

Seasonal allergies can sometimes lead to or be associated with other conditions, such as:

Living with seasonal allergies can be challenging, but preventing and managing your symptoms is possible. Try to monitor pollen levels and plan outdoor activities accordingly. It can help to reserve outdoor activities for when pollen levels are lower (in the late afternoon). If your allergy symptoms don't respond to treatment, consider consulting an allergist for advanced treatment options.