Hello! Welcome to HealthcareMagic! I have gone through your question and understand your concern. The cause of scab is unclear with no medical history (like if the patient is diabetic or hypertensive or currently on any medications or history of family allergies etc). However, a few causes considering the age and obesity can be enlisted. The most common on the list is fungal infection which you already suspect.Fungal infection can cause intense itch which eventually cause scab formation and may also leave a hyperpigmented patch over the area. Fungal infections are not due to unhygienic personal habit in most cases. In obese it could be the underlying diabetes, low immunity, excess sweating or even frequent use of antibiotics to treat other infections. It could even be a scab from healed decubitus ulcer. Decubitus ulcers appear to be more prevalent in obese patients who spend above average time on their backs. Wound healing is also slow in obese patients and even boils over the skin tend to stay infected for a long period of time with slow healing rate. Psoriasis also occurs more frequently in obese, but the reasons for this are unclear. These are only few causes, they are plenty others. Obesity and skin infections can cause low self esteem and depression which will prevent the patient from seeking any medical help. My advice is to address the issue to a GP as the scab have to examined to come to a diagnosis(like Wood s Lamp examination or biopsy or scrapping of the scab). At your visit expect a few basic test like blood sugars, ESR, thyroid levels and physical examination before concluding the underlying cause after which treatment will be initiated. Hope this clarifies you concern. Thank you for the query. Take care Regards, Dr. Ayesha Shareef, General & Family Physician