Bruise or birthmark on 3 1/2 week old

[Gangle]

Yesterday we noticed a reddish/purplish mark on DS's forearm in the shape of two lines. We initially thought it was a bruise and were wondering how on earth it got there but are now thinking that it could be a birth mark due to the shape and colour and because we don't know how he could have bruised himself. How can you tell the difference between a bruise and a birth mark?

DS was born with a mongolian black spot on the base of his spine. It looked just like he had a massive bruise and we were worried it looked like we were abusing him. Thankfully it faded when he was a toddler.

A bruise would change colour and go yellow as the blood disperses.

mongolian blue spots are only on bums/bases of spine.

a bruise will fade and go away.

No mongolion spots can be all over the body, but they are usually on the spine or the bottom.
I was just pointing out that birthmarks can look like bruises.

oh, sorry, just thought thats the only place iyswim. yes my ds2 has one and it does look like a bruise.

when my ds was born he had what looked like a scar just under his nipple,asked midwife what it was and she said its a birth mark.if your still unsure get it looked at by your health visitor

we noticed a purpleish mark on my ds's abdomen, and like you thought it was a bruise. It was not there at birth and we only noticed it from about 3 weeks. I was worried sick but showed the midwife who said it was a birth mark. It was only slight but noticeable with a defined edge. She said it may fade altogether or darken over time. Nothing to worry about. He is now 11 wks and has all but disappeared. Try not to worry but do show midwife or health visitor. How old is your ds?

My DD has a birthmark like this, and it has started to fade (she is 12 weeks). One thing though - the midwife who said it was a birthmark said to take a photo of it in case anyone in the future thought it might be a bruise - it is sad that we have to think like this but might not be a bad idea