When you're dog is outside a lot like in grass or wooded areas make sure you when you pet them you check down on their skin occasionally. Check for ticks, cuts, or abnormal areas.
I found this 'bubbled' spot on my doxie one time. Turns out it was an infected cut and he needed antibiotics. Also, I was at my groomers and I was petting their pet yorkie under the neck. There was a lumpy area. I told her and she felt it. She had no idea it was there. I dont know the result but I knew she left shortly after to the vets.
So love and pet those babies!