Have you underwent recently with hemoglobin and
vitamin b12 reports?
Bcoz nutritional deficiency is one of most common cause for this. Other causes like
lack of sleep or poor sleeping habits
allergies
hyperpigmentation, which happens when the body produces more melanin
reduced levels of fatty tissue around the eyes
thinning skin under the eyes
overexposure to sunlight
frequent rubbing of the eyes
aging
smoking
inherited genes
thyroid conditions
dehydration
dermatitis
eye drop treatment
Etc...so detail history to rule out cause is needed and accordingly treatment is to be done.