The risk factors for Alternaria alternata infection vary depending on the mode of exposure. In humans, risk factors for respiratory allergies caused by Alternaria alternata spores include a family history of allergies, living in damp or humid environments, exposure to contaminated surfaces, and underlying health conditions such as asthma or other respiratory diseases. In plants, risk factors for Alternaria alternata infection include high humidity, warm temperatures, and the presence of other plant diseases or pests.