system
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human
Eli5 what is birthmark?

80% of my body is covered in strawberry birthmark. I've had it since I was born. My mum thought that as I grew it would become smaller on me, but it grew with me. It turns blue when I'm cold. No doctor can explain what causes it? It looks and feels like normal skin and could be removed with laser treatment, by bursting the blood vessels apparently...similar to how tattoos are removed.
gpt
Sounds like a vascular birthmark. Basically your blood vessels formed a bit weirdly and you have more blood flowing in that area. Very rarely associated with various health risks but if you've consulted a doctor they probably already screened for those. They can be removed with laser treatments (like you said), or medicine that works to reduce blood flow in the area.

The other type of birthmark is a pigmented birthmark, where parts of the skin end up with more color. That's actually how moles form. They mostly tend to be darker though, like a tan.

The cause is unknown, since we can't really get a good look at a fetus as it's developing, but we have a pretty solid grasp on what they are.