Is doughnut effect caused by fluid buildup in the skin or in the penis tissue


Been reading a lot of posts here and also searching on this forum, firstly I am amazed by the wealth of data here!

I have a question which I couldn’t seem to find an answer to whilst searching. I was reading about the doughnut effect and people mention about this fluid buildup behind the glans.

Can somebody clarify if this fluid in building up in the foreskin or inside the actual shaft itself??

I am un-circumcised and when doing jelqing I find that I experience a build up of fluid in my foreskin and surrounding area that makes it very thick and sort of squishy. It’s not the actual shaft it self as I can feel that is relatvely the same size but slightly bigger from jelqing.
This fluid stays under the skin for a couple of days and then seems to dissapear.

Is this a sign that I am jelqing too hard and could be working towards this doughnut effect?