Hello,
From these symptoms it looks like seborrheic dermatitis. Seborrhoeic Dermatitis is believed to be an inflammatory reaction related to the proliferation of normal skin habitant Malassezia – a yeast, which produces toxic substances that infect and irate the skin. The disease is neither contagious nor related with diet but it may be aggravated by other illness like Psychological stress, immune compromised patients, neurological diseases like Parkinsonism and stroke.
Treatment usually involves use of antifungal, anti inflammatory and sebo suppressive or Keratolytic ingredients. Dermatologist also recommends the use of photodynamic therapy which involves the usage of UV- A, UV- B laser and red or blue LED light to inhibit the growth of the yeast and reduces the inflammation. If symptoms do not improve with ketoconazole then these treatment options can be planned.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Oxycodon can cause an immediate hypersensitivity reaction with itching. But then as to chronic itch, unlikely.