White discharge from a turtle's head may be normal, but it may also be a sign of a health problem. If the discharge is minimal and not accompanied by other symptoms, such as loss of appetite, decreased activity, difficulty breathing, etc., then there is usually no need to worry too much.
However, if the discharge is heavy and persistent, and the turtle's behavior or appearance changes, then there may be some health issue. These problems may include infections, parasitic infestations, malnutrition, and more. If you notice this, consider consulting your veterinarian for further diagnosis and treatment.
