A blue vein has appeared down the center of my nose. Why is this happening and is there any treatment?

 Unfortunately as the skin thins with age, we start to see the underlying veins on our face, arms and everywhere else on our body. Central facial veins, such as those on the nose are very stubborn to treat and I classically don't treat them. If I did, I would use a long-pulsed 1064nm laser, not sclerotherapy.

There are many potential causes of nasal veins including genetics, sun exposure, medications and aging.  There are also many potential treatments including laser, sclerotherapy, fine needle radio frequency, VeinWave and VeinGogh.  See a vein specialist.

A picture would have been very helpful in providing guidance.Most of these occur on the bridge of the nose.Not common for the veins to course down towards the tip of the nose.Repost your query with a picture. 

I would need to look at a photo to give you an opinion.  Otherwise, I have no idea what you are talking about.