Thomas might possibly have undiagnosed OCD (Obsessive compulsive disorder)
From Google
Obsessive-compulsive disorder (OCD) is a disorder marked by uncontrollable and recurring thoughts (obsessions), repetitive and excessive behaviors (compulsions), or both. OCD symptoms can begin any time but usually start between late childhood and young adulthood.
Although is not ok to diagnose people i think it's very possible to consider this. Basically one of the main behaviors of OCD is obsession with cleanliness and cleaning dirt.
For abused kids is very common to be obsessed with cleanliness bc they feel "dirty" and "unworthy" after they were abused so they feel compelled to clean themselves constantly.
People around Thomas example Dieter also said that Thomas is obsessed with cleanliness and is always clean.
Of course we need to make a difference having a hygiene and obsession for order and cleanliness. Thomas also admitted in his book and in some newspaper article from over 20 years ago that he felt disgusted to shower with other boys in the camp and use the soaps.
He also admitted to feeling sick while travelling by bus or being with a crowd full of people (can be a sign of claustrophobia?)
While claustrophobia is not actually proven to be a consequence of sexual abuse, sexually abused people relation with OCD can actually be backed up by studies
From the same source:
Furthermore, individuals with childhood sexual abuse histories are nearly seven times more likely to have an OCD diagnosis compared to those without a history of childhood sexual abuse (Saunders et al., 1992).
On Google there are plenty of studies that support the theory that a lot of sexually abused kids develop OCD later on.
Which for Thomas as someone who was sexually abused in childhood/teenage years makes sense.
There are also studies on the links of OCD and PTSD...
I had someone telling me the same thing about someone else with OCD and claustrophobia having links to sexual abuse so it wasn't about Thomas... It's definitely a high possibility. Although we shouldn't treat it as a certain fact but rather as something to keep an eye on since diagnosing is really a difficult thing and is done by those who are specialized. Thomas might also not have OCD but he definitely has trauma from the abuse and it makes him feel dirty. That's pretty normal reaction.