Oral ulcers and thrush are somewhat different. First, oral ulcers can occur in people of any age, but are more common in the elderly and children, mainly due to a low immune system. Thrush, on the other hand, commonly occurs in infants within the first six months after birth, mainly caused by an infection with Candida albicans. Clinically, oral ulcers may present with redness, swelling, and significant pain. Thrush is an infection by Candida albicans that occurs on the newborn's tongue, which may affect the infant's feeding, causing crying or refusal to eat. Generally, thrush is caused by an infection with Candida albicans and is a type of fungal infection, whereas most oral ulcers are due to poor nutrition or unbalanced nutrition.