Hello, It is good to know that you have no health problems. The bilateral dark marks that you noticed along the bra line commonly is a fungal infection, Intertrigo that appears in women with large breasts or it may also appear in large skin folds where the skin surfaces rub against each other. It is treated by keeping the skin clean and dry in the affected area. You can take oral antifungals(a course of fluconazole) or steroids. Apply antifungal/antibiotic topical ointments. However, you are suggested to visit a dermatologist & get physically examined before taking any oral medicines. Another medical condition that has a similar symptom is Acanthosis Nigrans, discoloration in the body fold & creases. Get examined & evaluated. Apply medicated lip balm in your lips & take vitamin B. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Nupur K, General & Family Physician