What Causes "air" Under The Skin?

i do home care- my client has what she describes as air under her skin. she says its all over her body & feels like they travel. she says they are about the size of a pinpoint each & millions of them. she can also "pop" them. they are driving her crazy, we have been to several doctors & specialists who cannot tell us what they are. they say she doesn't have them but my client is miserable.