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A harmful algal bloom (HAB) occurs when toxin-producing algae grow excessively in a body of water. Algae are microscopic organisms that live in aquatic environments and use photosynthesis to produce energy from sunlight, just like plants. The excessive algal growth, or algal bloom, becomes visible to the naked eye and can be green, blue-green, red, or brown, depending on the type of algae.

A change in season can brighten your days with vibrant new colors. But blooming flowers and falling leaves can usher in more than beautiful backdrops. Airborne substances that irritate your nose can blow in with the weather. When sneezing, itchy eyes, or a runny nose suddenly appears, allergies may be to blame.

Read about the negative health effects of particle pollution — and find steps you can take to prevent them.

Learn how ground-level ozone can harm your health — and what you can do to protect yourself.

Air Pollutants

Find information on public health issues related to air quality, including asthma, heart disease and stroke, and more.

Air Quality and Emergencies

Air pollution is a mixture of natural and man-made substances in the air we breathe. It is typically separated into two categories: outdoor air pollution and indoor air pollution.

Dust mites are tiny microscopic relatives of the spider and live on mattresses, bedding, upholstered furniture, carpets and curtains.

Many people think animal allergies are caused by the fur or feathers of their pet.