Gererally speaking, there are three reasons can lead to dark circles. As we know, the skin of our eyes are much more thinner than other parts. so is baby. So it is blood vessels under the skin which cause dark circles. In fact, this situation is quite normal and many babies have such appearance. In addition, your baby's skin may be much more thinner than others, so it makes more obvious. and if your baby does not get enough sleep, this situation will get worser. Here goes the second reason, which I believe you should pay more attention. Nasal congestion can also cause dark circles under baby's eyes. This combines to allergies. When allergies happens, it always accompany with a runny nose, red or watery eyes, ear infections and dark circles. So if this happen, you should pay more attention to potential allergen, like dust, pets, mold and pollen.
It is normal in some cases that little babies may get dark circles under their eyes. There are a number of reasons why your baby has dark circles under his eyes. The skin under the eyes of human beings is much thinner than that on the rest of the faces of human beings, which means blood vessels under the skin can make the area around the eyes look darker. It's possible that the skin around your baby's eyes is even more transparent than on other babies which will make the dark circles under his eyes more obvious. Tiredness can make the dark circles stand out even more. If your baby is very tired, his complexion may look paler. This will make the blood vessels underneath his skin look darker. Besides, if your baby has a darker skin tone it could also give the appearance of circles under the eyes. And occasionally, dark circles are caused by something other than skin tone, like allergic conditions, such as sinusitis or dermatitis, could cause dark circles. Talk to your health visitor or GP if you are worried.
A number of causes exist behind why your baby may be experiencing dark circles under her eyes. One example is that allergens, such as pollen, pet dander or mold, have entered and irritated the nose. Another is the existence of chronic sinusitis, which is a condition where the sinus cavities, which are hollow areas on the sides of the nose, fail to properly drain and become filled with bacteria and other irritants. Enlarged adenoids also could be to blame. If you notice your baby is frequently breathing through her mouth, enlarged adenoids could be to blame.