DS has a whole routine: suck right thumb while twirling hair with left hand (see Fig, A). He used to only do it when he was tired and it was kind of cute. But now he does it all.the.time. He won't wear hats because that interferes with the hair twirl. From the minute he wakes up, the thumb is in his mouth. While eating, thumb is often in the mouth in between bites. I have to pry his thumb out of his mouth to get his shirt on. When we go for a walk, I try to hold his right hand...but then he will get annoyed because he can't suck his thumb. There is now a callus on his thumb.
I'm afraid what started out as self-soothing has now also become a really bad habit. I know he's too young for thumb guards and nasty tasting liquids, etc. but I have to say... I've had it with the thumb!
(Fig. A)

Re: Who has a thumb-sucker?
I would have a thumb sucker if it weren't for the pacifier. Nate is attached like this to his "bah." If we take away the pacifier, then the thumb goes in the mouth instead! I have an ultrasound pic of him in utero sucking his thumb! He came out with sucking blisters on his lips.
We have a thumb sucker, but it's only when he's tried/sleeping. Or if he has his blanket that he sleeps with (then it is carry the blanket all over the house while sucking his thumb - so we try really hard now to keep his blankie in the crib so it's only for sleep times).
When he's teething he definitely sucks it more - so it gets callused or even becomes an open sore (lovely, right?). But once his teeth seem to come in he backs off and it heals up. One time when he had his 4 top teeth coming in all at once and it got really bad we put a band-aid on it while he was awake to keep him from sucking it. We took the band-aid off during naps/bedtime. That seemed to help.
DH asked about it at his 18 month appt and the pedi said that at this point there was no reason to worry about it. That most kids give it up on their own by age 3. And last time I was at my dentist I asked him about it and he said that it wouldn't affect his teeth until his permanent ones starting coming in around age 5-6-7. But DH and I both had really crooked teeth as kids and had to have braces (and neither of us were thumb suckers) - so I feel like braces are going to happen for DS no matter what we do.
Isaac is a finger sucker. All of my kids either sucked their thumbs or their fingers. We ended up buying the finger nail stuff to help them quit. It worked really well with 3 of the 4 kids. I still occasionally catch my 6yo with her thumb in her mouth, but it's rare enough that I don't worry about it.
Won't use anything on Isaac to help him quit until he's at least 2 or so depending on how often he does it.
I have a thumbsucker. I am not worried about it. At first it was constant, the last month it has been getting less and less. Yes he has a callus on his thumb- but so did I (on my finger) when I was in college from taking constant notes- it went away in a few months so I am sure his will go away quickly.
And I believe that as long as he stops by the time his adult teeth come in then all is good. Plus I am not all worried about braces- many many kids get braces for things other than sucking their thumb- it is not the end of the world.