Most fungal infections are transmitted by contact with animals or other persons who have the condition. Some fungal infections are airborne, meaning you breathe in the fungal spores. People with weakened immune systems can become symptomatic from the fungus (yeast) that naturally lives in your body. "Thrush" or some types of diaper rash are also caused by fungus that naturally lives in your body.

Shelley C. Springer, MD, MBA, MSc, JD, FAAP

He can get it from other people, from fungus in soil or the environment, from sweaty shoes, from the shower where someone has showered with feet fungus,etc. Just about everywhere