I had a serious breakdown some years ago, and have found it difficult to shower ever since then.

Sometimes I have to write out the steps involved, and then make myself follow each step.

Sometimes I think it is because it is 'isolating' to be in the bathroom with the door shut and the water running.

Sometimes if I pamper myself a little bit ahead of time, that can help. Sometimes I need to eat something first. Or to get warm.

From time to time it has helped me to write down that I don't want to take a shower, and to write out how I feel about it. Then it will be easier to get started.

Sometimes I use a list of three simple steps:
1: Lay out the clothes I will put on afterward. (I like to do this, and it does help.)

2: Put on some great music. (My personal preferences are Beach Boys and Creedence Clearwater Revival.)

3: Turn on the hot water.

So I've accumulated a number of little tricks to help me get get going and get into the shower. They all help, but there's still almost always that bit of resistance.

Actually, I think there are quite a few of us who are shower-resisters. Sometimes it has to do with depression, but I think it often has to do with isolation.