Hello, Dark itchy lines under the arms or itchy moles are usually harmless but at times they can be cancerous. You can get clinically examined, get biopsy done to rule out any malignancy. In the meantime, take care of your hygiene, take regular bath and wear soft cotton clothes. You can apply a thin layer of ointment Hydrocortizone on the itchy areas. You can also apply Neosporin ointment or Soframycin ointment for relief. If its fungal infection, take a course of fluconazole. Do not touch or scratch the moles. Most moles cause no symptoms and do not need treatment. But moles that are itchy, painful, large or suspicious for cancers may be recommended by your treating doctor to be removed. It will be done by him. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician