Are marmoset monkeys bald under their armpits?

Marmoset monkeys do not have fur under their armpits. They have hairless areas under their arms, just like humans.

This is because marmosets use these areas for scent marking. They have special glands that produce pheromones, which are chemicals that send signals to other marmosets, like information about their sex, social status, and even their health.

So, while they might look bald, it's actually a very important part of their communication and social life!