Spider veins or varicose veins: where exactly does the line fall on your legs?

You step out of the shower, catch the inside of your calf in the mirror, and there's a web of fine lines that wasn't on your radar last summer. Or maybe it was, and you've been quietly waiting for it to fade. Either way the first question is rarely cosmetic. It's whether something has started.

Leg veins get confusing because three different things share the same everyday name. A fine red line sitting just under the surface, a slightly thicker blue net a layer deeper, and a rope-like vein you can actually feel with a fingertip all get called "veins on my legs" — but they sit at different depths and they ask different questions of you.

So the first thing worth sorting isn't color. It's caliber, plus whatever comes with it. Varicose veins are defined as engorged, tortuous vessels larger than 3 mm, while thread veins under 1 mm and blue reticular vessels of 1 to 3 mm are classified separately. Plenty of legs have both at once, which is exactly why lumping them together leads you down the wrong road.

This article organizes treatment information to STON Clinic standards. Individual results vary, and whether a treatment suits you is a decision to make with a board-certified dermatologist.

Why those fine lines show up on the calf and behind the knee

Why those fine lines show up on the calf and behind the knee

Nothing new has grown. What you're seeing is a vessel that was always there, now wide enough to be visible through the skin. Telangiectasia* describes very fine vessels in the skin that have dilated into visible red lines, and when the same area reads blue instead, it's because slightly larger venules are involved and the finding gets its own name.

Telangiectasia: very fine blood vessels within the skin that have widened enough to show as visible red lines. The blue version involves venules and is called venulectasia, or reticular veins.

DermNet draws that distinction by color and by which vessel is doing the work: the red linear ones involve capillaries, and visible small vessels that look blue are called venulectasia because venules are involved. The same page lists the backgrounds that commonly overlap — pregnancy, accumulated sun damage, topical corticosteroid use.

None of this is rare. On the varicose side, the reference notes that approximately one-third of men and women aged 18 to 64 years have varicose veins, with age, pregnancy, body weight, prolonged standing and family history all named as contributors. Which makes "why me" a less productive question than "which stage is this."

Why those fine lines show up on the calf and behind the knee

Thread veins, reticular veins, varicose veins: what does the size gap actually tell you?

Thread veins, reticular veins, varicose veins: what does the size gap actually tell you?

Caliber comes first because it's the one thing you can assess without equipment. DermNet's thresholds are 3 mm and above for varicose veins, under 1 mm for thread veins, and 1 to 3 mm for reticular vessels. The same page adds something people rarely hear: the two smaller categories aren't detected on duplex ultrasound. What's visible and what's measurable don't fully overlap.

Symptoms are the second axis. Varicose veins are tied to valves that no longer hold, so blood refluxes downward, and that's the version that tends to arrive with heaviness, a dull ache, itching, or legs that feel tired by evening. Thread veins on their own usually come with no complaint other than how they look. The NHS makes the same split, describing thread veins as small red, blue or purple veins that are usually harmless and treating them separately from varicose disease.

The third axis is the skin itself. On the varicose side the listed complications include dermatitis, skin that hardens, ulceration, and bleeding. If any of that is in the picture, the order of operations changes completely, because something now outranks appearance.

Why STON Clinic writes down your symptoms before counting the veins

Why STON Clinic writes down your symptoms before counting the veins

The first questions in a leg-vein consultation aren't about how many vessels there are. We note when you first saw them, whether your legs feel heavy by the end of the day, whether there's any tingling or swelling in the calf, whether your work keeps you standing, and whether a pregnancy or a weight change lines up with when it started. Appearance can't tell us what the valves deeper down are doing.

Next we place what's visible into a caliber band and look for anything on the skin itself — a patch that has changed color or hardened, a sore that hasn't closed. When heaviness, swelling or skin change turn up alongside the veins, we say so plainly: an assessment of vein function comes before any conversation about the surface. Clear the visible part while reflux remains and the same area can refill.

We don't promise a result. What we commit to is order and record-keeping. The symptoms and the spread recorded at a first visit get rechecked against the same list at the next one, and that record is what decides whether the surface is the right place to work or whether vein assessment comes first.

How does the treatment process run, step by step?

How does the treatment process run, step by step?

Start with something that saves disappointment: lifestyle changes don't erase vessels that are already visible. The NHS lists elevating the legs, cutting long stretches of standing or sitting, weight management and moisturizing as the general measures — while also noting that treatment aimed at improving how the veins look isn't usually provided within the public system. Appearance and symptoms are handled as separate tracks, and it helps to plan them that way.

For surface vessels there are two main options: sclerotherapy, which closes the vessel with an injected agent, and lasers that are absorbed selectively by the vessel. A 2021 Cochrane systematic review pooled the evidence for thread and reticular veins across 35 randomized trials with 3,632 participants and found moderate-certainty evidence that sclerosing agents produced more resolution or improvement than placebo.

The same review is equally clear about the downside. Hyperpigmentation and matting were reported more often with sclerosing agents than with placebo, and when laser was compared head-to-head with sclerotherapy there was no clear difference in how much cleared — though pigmentation showed up less often on the laser side. That isn't a verdict for one method. It's a choice about which trade-off you'd rather carry.

How does the treatment process run, step by step?

The review also notes that the small number of studies and participants in each comparison limited confidence in the findings. So rather than fixing a session count in advance, it's more realistic to treat one area, watch how any pigment change settles, and widen from there.

Three things to check the next time you look

Three things to check the next time you look

Caliber first. A fine line under a millimeter, a blue net at one to three, or something raised above three millimeters each point somewhere different. Photographing it from the same distance makes the next comparison far easier than memory will.

Then name the complaint honestly. If it's purely how the leg looks, that's one track. If your legs are heavy and swollen by evening, vein function comes first. And a sore that hasn't healed in two weeks, or any bleeding, doesn't wait its turn in the queue.

Last, change one thing at a time and write it down. Standing hours, leg elevation, how much area you treat — alter them together and you'll never know which one mattered. One change, one note, and the moment to add a step becomes obvious on its own.