Dermaviduals: Apart from the sun, what causes Dark Spots?
Dark spots on the skin, also called hyperpigmentation, are a common skin problem. There are a variety of conditions and agents that can cause them to develop. One of the most under-recognised causes of dark spots is post-inflammatory hyperpigmentation. This occurs after some type of trauma to the skin – especially infections like acne.
Source: Dermaviduals Australasia,
https://www.dermaviduals.com.au/faqs/apart-sun-causes-dark-spots/