Yes, fat can become thinner with treatment of corticosteroid injections into the deep dermis or subcutaneous compartment dependent on concentration and dose and the patient's metabolism. There are treatments to improve the condition should it not improve spontaneously, such as fat injections, depending where on the body the atrophy is located. There are other causes of fat atrophy including acne cysts that get so inflamed that without the steroid injection, when the cyst goes away there is an indentation that is seen and felt! Some cysts need to be injected with steroid otherwise they would become bigger and the indent even larger, so that indent is not a result of the steroid injection usually. Some hypertrophic scars are injected with steroid and when the scar improves, there can be an indent by itself without steroid, but some of these scars need steroid injections and if there is atrophy later, it could have been the scar itself.