Thrush: what are its symptoms and why does it appear? 2026

You may notice the baby is very fussy during feeding and, in addition, you notice the presence of some white spots in his mouth. If so, it is possible that the child has a yeast infection popularly known as thrush, although the reality is that it is an infection known medically as oral thrush.

Of course, the name should not scare you, since it is very common among the little ones. However, if you have ever experienced a vaginal yeast infection, you can probably imagine the discomfort your little one may feel. Therefore, what is thrush, what are its causes, what symptoms arise and how can we help the baby feel better?

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What is thrush?

Oral thrush is a type of infection of the oral area caused by a fungus or yeast called Candida albicans, which generally causes the appearance of white or yellow spots or sores, irregular in shape, that cover the gums and tongue, as well as the lips.

This is a mild infection, although it can be uncomfortable and even painful for the baby. In addition, the infection can also be easily transmitted to the mother if, for example, she is breastfeeding.

What are the causes of thrush? How do babies get infected?

Although the fungal infection known as thrush or oral thrush appears in the baby's mouth, it possibly began in the birth canal as a fungal infection. It was there that the baby contracted it the moment he made his way into the world.

Candida, as you probably know if you have suffered a vaginal yeast infection at some point in your life, is an organism that we normally find in the mouth and vagina, but in quantities that do not cause any type of problem, and are also controlled by other microorganisms. But when you get sick, start taking antibiotics, or experience some type of hormonal change (as happens during pregnancy), the balance can be upset, allowing Candida to grow and cause infection.

In any case, thrush appears especially in newborns and babies under 2 months old, mainly because it is an infection that is picked up at birth.

But this does not prevent slightly older babies from also suffering from it, especially if they have been taking antibiotics in order to combat another infection. As you know, although antibiotics are necessary to treat infections of bacterial origin, they also tend to eliminate the “good” bacteria that keep yeast under control.

It can also develop in the mother's breast when it does not dry properly after feeding, giving the yeast an excellent opportunity and environment to grow, eventually causing infection.

Pacifiers and bottles may also be a related cause, as they can overly moisten the inside of the baby's mouth, also providing the perfect environment for yeast to thrive and grow.

How to know if the baby has thrush? What symptoms appear

White patches that appear in the baby's mouth or tongue can be a symptom of thrush, or they can also be caused by milk residue, which tends to remain on the baby's tongue after feeding. However, they generally dissolve within an hour.

Therefore, to know if the baby's white tongue is caused by milk or this type of fungal infection, you can try to gently clean it with the help of a soft, damp cloth, or with a finger covered with gauze.

If the tongue is pink and looks healthy once we have cleaned it, it is not necessary to carry out any type of additional treatment, since the whitish patch is actually caused by milk residue. However, if the patch does not come off easily, or if it does and you find a reddish area underneath, it is probably thrush, and you should tell your pediatrician.

Is it contagious?

If the mother is breastfeeding the baby, there is a risk of fungal infections being transmitted from one side of the baby's mouth to the other and, subsequently, to the mother's breast during different breastfeeding sessions.

If the infection also occurs in the mother, the symptoms of nipple thrush include burning and pain in the nipples, redness, itching, and the appearance of scaly and/or crusty patches. Shooting pains may also be felt in the breast, either during or after feeding.

On the other hand, it is also possible that when the baby has oral thrush, he or she may also end up with diaper rash due to a yeast infection.