Dark circles under the eyes happen due to aging, genetics, lack of sleep, allergies, or dehydration. The skin around the eyes is thin, so blood vessels and pigmentation show easily, making the area look darker. Common signs include discoloration in shades of blue, brown, or purple, and puffiness that makes you look tired. Poor sleep, stress, sun exposure, and rubbing your eyes can make it worse. Proper care like drinking water, sleeping well, using cold compresses, and applying eye care products can help reduce dark circles and keep the under-eye area clear.