Vanillylmandelic acid, or VMA for short, is a substance found in pee. Pee is the yellow liquid that comes out of your body when you go to the bathroom.
VMA is made by your body when it breaks down certain chemicals in your body called neurotransmitters. Neurotransmitters help your brain send messages to the rest of your body. When your body is done using these neurotransmitters, it breaks them down and gets rid of them through pee.
Doctors can look at the amount of VMA in your pee to see if there might be a problem with your body breaking down these neurotransmitters. This can help them figure out if there might be a problem with your adrenal glands, which are tiny organs in your body that help regulate hormones.
So basically, VMA is a substance in pee that helps doctors check if everything is working right in your body!