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Symptoms of Thread Veins

They appear to be easy to identify – but why do the symptoms of thread veins vary so much in colour and size?


The visible symptoms of thread veins appear as many different sorts of marks and depths of colour on the legs, depending on the size and distribution of the thread veins themselves. Vein walls are naturally white, so if they are empty of blood, thread veins are not seen at all under the skin.

But once they fill with blood, thread veins can range from being so small and pink that they can look like an early bruise on the leg to being so large and dark blue that they resemble the blue veins in a Stilton!

The colour of the thread vein depends on the size of the vein itself; whether the blood within is flowing or stationary; and its depth relative to the surface of the outermost ‘dermis’ layer of the skin.

Very thin thread veins can appear to be red or pink, because the blood flows through them fairly well. And if they are very near the surface of the skin, the colour of the blood is seen as the colour of the vein. If these very thin thread veins lie much deeper, then they are not seen at all from the surface.

When thread veins are larger in size, blood flows more slowly within them, giving up more oxygen as it does and so they appear darker red. In some thread veins, especially those nearing 1mm in diameter, a layer of blood can clot and stick onto the thread vein wall. This layer of clotted blood (or ‘thrombus’ as it is known) causes the thread vein to look much darker still – usually dark purple or dark blue if near the surface.

The depth of the vein under the surface of the skin also has an effect on the colour of the thread vein. When the thread vein is very near to the surface, it can be seen clearly and the colour is bright. The deeper the vein is in the dermis, the less distinct the vein and the more hazy the colour.