It’s quite difficult to explain.
Do you try to tell them in medical terms?
That we have two trigeminal nerves, one for each side of the face.The trigeminal nerve is a paired cranial nerve that has three major branches: the ophthalmic nerve, the maxillary nerve, and the mandibular nerve.
One, two, or all three branches of the nerve may be affected. It can affect one side of your face, and occasionally both sides.
The pain may be felt in the ear, eye, lips, nose, scalp, forehead, cheeks, teeth, or jaw and side of the face.
It can sometimes be caused by a compression on the nerve, possibly by a blood vessel or artery. Sometimes, there is no known cause.
Then do you add this bit?
Trigeminal Neuralgia is one of the most painful conditions known to mankind and is sometimes referred to as the Suicide Disease.