Welcome to HCM,
You are having lighter patches on chest and abdomen.
Lighter means hypopigmented.
They are increasing and after hot bath there become redness around the patches.
After such history I feel you may be having either tinea versicolor
or pityriasis alba
Both the conditions are mild and benign.
Tinea versicolor is superficial fungal infection
caused by Mellasezia furfur..
Pityriasis alba is superficial eczema... And caused by sunrays,dust,worms or infection..etc
Antifungal tablets and cream may be helpful in tinea versicolor.
And pityriasis alba may respond to mild steroid
or tacrolimus and remove the suspected cause.
You contact dermatologist
for firm diagnosis and treatment ..
I hope you got my answer.
Dr. Ilyas Patel MD