What can cause breaking out on the tongue?

Many things. Oral lesions of the tongue can caused by different things: oral thrush is from a yeast infection which presents as white covering of the tongue; herpes and other viruses. The most common problem is apthus ulcers (canker sores) occurs for one or multiple reasons (stress, harmones, infections, etcs) there are different formulations of mouthwashes that can be prescribed.
Many Causes. Tongue sores can be caused by infection, stress, poor dental hygeine, or occasionally cancer. If the sores persist you should see a doctor.