My son smells like vinegar

[Guest guest]

Hello everyone,

a few days ago, my son's neck smelled very strongly of vinegar. We don't use vinegar so I went through the house looking for a reason...an old cleaner, a toy, etc. I thought it could be his clothes so I washed it all and gave him a bath and the smell was gone. Today it's back! But it's his forehead this time. You can't miss it, it's a very strong clear smell of vinegar.

Anyone know what this is? What is causing it? Is it good or bad?

TIA,

Stéphanie B.