Noticing a growing black mark on your chest is important and should be evaluated promptly by a dermatologist, as it could represent a variety of skin conditions, including potentially serious ones like melanoma.

What you should do:

• Schedule an appointment with a dermatologist as soon as possible for a thorough skin examination.
• Avoid self-treating or applying any medications without professional advice.
• Monitor the mark for changes in size, shape, color, or if it becomes painful or bleeds, and seek urgent care if these occur.

If you notice any rapid changes or symptoms like bleeding, pain, or itching, consider visiting an emergency dermatology service immediately. Consulting a specialist will ensure accurate diagnosis and appropriate management.To narrow down potential causes, we will need some more information.I understand you're concerned about a growing black mark on your chest. To give you the best advice, could you please tell me your age and gender?