Noticing black gums on your child can be frightening, but there are many possible causes. In general, milk ingestion isn't a direct cause of black gums, but it may contribute to periodontal disease that involves the gum line. Instead of banning milk from your child's menu, though, take precautions to help him keep his teeth clean and investigate other possible reasons for his discolored gums.
Periodontal disease occurs when bacteria grow in the mouth and build plaques, which damage teeth and gums. If the bacterial growth becomes severe, a condition called acute necrotizing periodontal disease can develop, in which the gums become black and die off. Periodontal disease in children does not usually progress to this level, although some kids get early onset periodontitis. Most of these cases involve immune disorders or genetic susceptibility. Like any other food or drink, milk can contribute to periodontal disease if the teeth are not brushed regularly or if the milk is allowed to pool in the mouth for long periods of time.
Because sipping milk off and on throughout the day or falling asleep while drinking milk can contribute to the development of periodontal disease, parents should avoid letting a child do these things. Don't give your child a bottle of milk at bedtime, and avoid giving him a bottle or sippy cup of milk to carry around with him as he plays. After drinking milk or juice, brush your child's teeth or have him brush them himself if he is old enough to handle the toothbrush.
In children, tooth eruption is a more likely cause of black gums than acute periodontal disease. The gums can become black and blue as the underlying teeth work their way up through the gums and try to break through the surface. Any minor trauma, such as biting down on a hard teething ring or piece of food, can cause a bruise that appears black, blue or gray. This commonly occurs in babies and toddlers during the eruption of molars or front incisors, but older children who are developing their permanent teeth may also get black or discolored gums.
Another extremely rare cause of black gums is oral melanoma, a form of cancer. You should have a dentist look at your child's mouth to rule out oral cancer or periodontal disease even if you think the discoloration is more likely to be the result of teething.