They creep up and down legs and thighs, around ankles and calves, but most of us think spider veins and varicose veins won't appear — if they appear at all — until we're older.

Much, much older.

Not so.

"It can happen at any age," says Dr. Craig Schwartz, with the Vein Centers for Excellence of Kansas City. "We've seen women in their 20s. I've even seen teenagers."

"Usually starts about age 20," says Dr. Neil Sadick of Sadick Aesthetic Surgery and Dermatology in New York.

But not to worry. Sadick and Schwartz give the lowdown on the difference between spider and varicose veins, what causes them, and how they can be prevented or treated.

SPIDER VS. VARICOSE

Sunburst or starburst-shaped veins that show over skin and have a purple or blue linear color are spider veins, Schwartz says. They're generally a cosmetic issue, and treatment isn't often considered a medical necessity, he says. They mostly appear on legs, but sometimes show up on the face too.

Large, bulging, dilated, ropey-looking veins are varicose veins, Schwartz says. They can lead to long-term clinical problems, such as chronic swelling, skin changes, bleeding, clotting and infection.

The good news: Just because you have spider veins doesn't mean you're definitely going to develop varicose veins, Schwartz says.

CAUSES

1. Genetics: The top cause, Schwartz says. "If you've got those genes, you're going to develop them almost no matter what you do," he says.

2. Pregnancy: Hormonal changes, the increase in blood to support the baby causes veins to dilate and the weight of the baby on major blood vessels all contribute to spider and varicose veins, Schwartz says.

3. Trauma: Sometimes factors from years ago, such as sports we played in youth, will traumatize areas that show spider veins 10 years later, Schwartz says.

4. Hormonal influences: Sadick says the hormone estrogen has an effect.

5. Sitting or standing for long periods of time: It's tough on the legs to stand on your feet all day — as it is to sit at a desk the whole day long, Schwartz says.

"Blood tends to pool in your legs, and it has a hard time getting out of there," he says. "As that pressure builds up it starts forcing that blood out little side branches and channels because that blood's got to get somewhere; it can't just stay there in your leg. It comes up to the surface it starts appearing as the dilated varicose veins or the superficial spider veins."

Sadick says it's just a myth, however, that crossing your legs causes spider and varicose veins. However, keeping your weight down can be helpful.

TREATMENT

Both doctors say there are minimally invasive ways to treat spider and varicose veins. All involve trying to get the veins to collapse and seal closed so the body can reabsorb them.

Spider: