If the tail is drooping as well, it can be something called "cold tail." It can be caused by swimming in cold water, though it is not generally understood why it happens. One of my dogs used to get this condition frequently. Its not really problematic, and usually goes away within a day. If it continues, you should probably see a vet.
This could be a cycst, burn, wart, ingrowing hair, scar tissue, or a cancerous or noncancerous tumur among other things. If you have only noticed it recently then it is not a reason to panic, but it would be wise to have it checked soon by a vet.
I thought my dog's swollen tail was due to anal gland problems. He did need them expressed but my vet told me that dogs store fat in the base of their tail, and that it's normal. An over weight dog will have much more. (my dog was 4lbs over weight)
However, if you dog has other symptoms related to his anal area, I would suggest calling your vet.
I hope this is helpful.
Anal glands if you don't know how to empty them ask vet or groomer to show you:)
There are several possible answers: Trauma, self-trauma, infection, tumor....The only way to accurately diagnose the problem is to visit your Vet.
Sometimes flea bites
What would cause a head pain when my head it more so turned to the right than the left?
Lowering a stream's base level will cause the stream to do what?
For example adding a base.
A cushion like swelling at the base of the leaf or leaflet.
Erode
Goitre is the disease in which thyroid gland swells up
A goiter, the large swelling at the base of the frost of the neck. is an abnormal enlargement of the thyroid gland.
Waves pounding the base of the cliff.
Lowering a stream's base level will cause the stream to do what?
Gummy bears have a gelatin base. Any liquid would cause them to swell, not just Sierra Mist.
If the base of the tail is swollen, it may be infected by a bite of another animal. The swelling will need to be drained by your veterinarian, and it may require antibiotics.
Trauma to the base of the brain can affect vital structures such as the brainstem, which controls basic life functions like breathing. Damage to the base of the brain can also disrupt the cranial nerve functions, leading to severe complications. In contrast, trauma to the frontal lobes may primarily impact cognitive functions and behavior, which are often not immediately life-threatening.