Hello,
Thanks for posting your query.
In order to give you the most probable diagnosis I would be appreciated if you can specify few details of your problem as follows,
1. Onset duration and progression of your symptom ( dark patches ).
2. Description of the lesion ( size , shape ,number , site , colour, etc)
3. Wether you are on any medications or have any significant medical history etc?
Assuming you have just recently noted flat patches of hyper pigmented skin around your waist and have no itching ,pain , or any other symptom ,this could be most probably an allergic reaction or dermatitis or eczema or due to sweat or friction.
If the patches are longstanding , itch , or are increasing in size and number then fungal infections and systemic skin disorders need to be ruled out.
The best way to confirm the diagnosis would be to get it examined by your dermatologist who can then start specific treatment depending on the cause.
Meanwhile you can apply calamine lotion at the site of the lesions and see if it helps. You could take some oral antihistamine medications like cetrizine or loratadine if there is any itching . You need to maintain a good personal hygiene & try to keep the region as dry and sweat free as feasible ( wear loose clothing ).
If these are due to eczema or allergy the above measures should provide some relief and gradually the lesions will resolve on their own .
Please avoid applying any cosmetic products on the affected area .
Hope I have answered your query.
Kindly accept my answer if you have no further queries.
Regards

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