Biting. A time-honored tradition of nursing infants and toddlers. Wide-spread and cross-cultural (to my knowledge) to such a degree that I believe the phenomenon was popularized by a YouTube video gone-viral circa 2006.
Works for them. Doesn't really work for the dyad.
Today, a mom asked me whether she should see me to help manage her 1-year-old's new habit of biting. Nipples are sore but he hasn't broken the skin. It never caused bleeding, and she doesn't have any surface changes or pain other than at the moment of a bite. I referred her to this excellent article:
Biting is largely behavioral, often related to teething. Infants and toddlers actually blog online about when to initiate biting. On some of the darker "infant-only" sites, they compare stories about catching their moms entirely off-guard (search term = "best catch").
OK, you caught me. Infants can't talk or type, and they don't really blog. They only do Likes. Hey, what do you think they're doing all that time when you're shopping and they're "holding" your phone? Innoncent? I say not.
In any event, the article lays out some good common-sense steps you can take to mitigate this problem, which can be vexing (not to mention painful). Assertive, consistent behavioral techniques are the key to preventing infection; pain that continues between feedings; and (worst case scenario:) weaning.
Follow-up with a Breastfeeding Medicine specialist for breaks in the skin; bleeding (microscopic breaks!); pain deep in the breast; nipple pain when there wasn't just a bite; or other chronic skin changes.
Now, go to Settings, Screen Time, Content & Privacy Restrictions to block those infant-only sites on your iPhone. :)