I tend to get sore thumbs from over-using my iPhone. Here’s something interesting that I noticed when I used an Android phone for 6 months. My sore thumbs disappeared. To tell you the truth, I didn’t really notice this until I switched back to the iPhone again, then after about 1 week my sore thumbs reappeared.
On both phones I was using my thumbs to type. So I think the difference is the iPhone home button.
It’s not a huge force that is required to press the home button, but because it needs to be pressed reasonably hard, and it is used a lot (every time you open a new app) it seems to give me sore thumbs.
So I’m excited about Apple’s move to get rid of the home button altogether with the iPhone X. Looks like they will be using an up-swipe to go back to the home screen. In the meantime, if you get sore thumbs, I’d suggest trying this trick.