Is a prominent vein near your temple dangerous?

Temple vein: No. It is low pressure blood vessel. Normal variant.

Multiple reasons.: Facial veins like hand veins often change in size throughout the day and is due to many factors such as hydration, sun exposure, hereditary, heat, physical activity, stress and anything that would make the veins dilate or constrict. There are also some medical conditions such as heart failure, kidney and liver failure which could contribute but not in a healthy 30 Y.O.

No: They are common and may not look bothersome. However they are just nuisance veins. Mostly a cosmetic concern.

Typically no: Prominent veins in this temple region are fairly common & typically benign. Temple veins often become more prominent as you age & the skin thins on the face & the veins dilate a bit. Weight loss can also make temple veins more visible. Only time a vessel in the temple area can be dangerous is w/ "temporal arteritis" (artery not vein) & often symptoms of pain / tenderness / headache are present.