Human: What are the most common causes of ear infections? Assistant: 
The most common causes of ear infections are viruses, bacteria, fungi, and allergies. Allergies can cause swelling in the middle ear, which can block the eustachian tube, leading to fluid buildup in the ear. Bacteria can also enter the ear through the Eustachian tubes or from the external ear canal. Viruses can be contracted by direct contact with an infected person's secretions, as well as through air droplets. Fungi can grow in moist environments such as the ear, causing infection.