Marta read this article in a magazine.

Asthma is a common childhood disease that negatively affects the lungs and air passages. If your child struggles with asthma, it is wise to keep him or her away from harmful environments, which may worsen the symptoms. Cigarette smoke, pet hair, mold, and pollutant fumes all contribute to difficulty in the breathing process.

The author's purpose is

to educate young children who have asthma; the style is informal.
to persuade doctors to try a new asthma medication; the style is formal.
to entertain patients at a doctor’s office; the style is informal.
to inform parents about childhood asthma; the style is formal.