Hi, I'm Craig and this is Mental Floss video. Today, I'm going to answer credyramos? big question: Why do people have birthmarks? 

Let's get started. I'm not going to show you my birthmark. 

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I want to start by talking what a birthmark is, before we get into why. A birthmark is a mark found anywhere on the skin. Typically people are born with them but sometimes they appear later -- and then they would be a later mark (not a birthmark). And there are few different types, which all fall into two categories: pigmented and vascular. 

Pigmented birthmarks are ones that result from extra pigment in one area. Basically the skin contains pigment cells and these birthmarks occur when pigment cells cluster together. (And how many times can I say pigment in this video?) Examples of these include: moles and cafe au lait spots, which are usually light brown spots. 

Vascular birthmarks appear when a bunch of blood vessels underneath the skin gather together in the same spot. Examples include: hemangiomas, which you might know as strawberries, and port wine stain, which are reddish spots. Usually vascular birthmarks are found on the head or the neck and their color depends on where the blood vessel clusters are. If they are close to the skin surface, the birthmark will be more red and if they are way below the surface, the birthmark will be blue. 

That kind of explains why birthmarks appear, but there are so many different types and they appear in so many different ways -- because of that experts still aren't sure of the exact cause or purpose. And interestingly some birthmarks are hereditary and some aren't. There are a few theories about why birthmarks exist though. We always got theories. 

They might have to do with certain proteins that the baby is exposed to in the placenta, but the mechanism is still poorly understood. Hemangiomas specifically, have been associated with low birth weight and one study concluded that a lack of oxygen and placenta during an embryo gestation might cause them as well. 

So now that I basically told you that birthmarks are a mystery, you might be wondering why they sometimes need to be removed or treated. They can be associated with medical problems. Like a birthmark might affect a person's ability to see, breath or hear. If a birthmark is getting larger while on an internal organ, that's a concern or if its just growing really fast it might be indicative of a tumor. 

Thanks for watching Mental Floss video, which is made with the help of all those hemangiomas. If you have a big question of your own that you'd like answered, leave it below in the comments. See you next week!

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