With Dr Samira Syed, associate specialist in paediatrics (dermatology), Great Ormond Street Hospital

Birthmarks are very common. In fact one in 10 babies has a blood vessel birthmark that is present at birth, or appears within a few weeks of birth. These are usually "stork marks" or strawberry marks, and they tend to disappear in time.

Other types of birthmark, including port wine stains, are less common but permanent.

Twenty years ago, treatment for permanent birthmarks consisted of advice on camouflage make-up. Today it's a very different story - thanks to tremendous advances in the use of lasers, these birthmarks can now be treated. For some children it can mean their birthmark improves significantly, especially if they are on the face.

Birthmarks are often worrying for parents and whatever sort of birthmark your baby has, it's worth getting an accurate assessment at an early stage. If it's a permanent birthmark, the sooner treatment is started the better - results are usually more effective the younger a child is.

What is a birthmark? A birthmark is a blemish on the skin and there are many different types. Some are present at birth, others appear in the first few weeks of life. They can be red (blood vessel marks), brown (moles) or blue-ish birthmarks. They can also vary in size.

What are blood vessel birthmarks? The most common are blood vessel marks known as "stork marks" and strawberry marks. They are caused by an abnormality in the way that blood vessels form just beneath the surface of the skin as the baby is developing in the womb. They occur spontaneously and, in almost all cases, are not inherited from parents.

"Stork marks" arise from the tiniest of blood vessels and are usually on the back of the neck, upper eyelids or in the middle of the forehead. They affect around one in 40 babies. Those on the face fade and generally disappear by the time a child is two years old. The ones on the back of the neck persist but do not pose a cosmetic problem because they are covered by hair. They tend to become pale or lighter into adulthood.

Strawberry marks, or haemangiomas, are not usually visible at birth. They appear in the first week or so and increase in size over a period of three to six months. Most are small and do not need any treatment. Around half disappear of their own accord, usually within the first five years. Occasionally they can cause problems because of where they are on the body - for example around the eye, mouth or genitalia - and will need medical treatment.

What are permanent birthmarks? Sometimes a birthmark is permanent. Port wine stains are a red or purple area of skin present at birth - they affect three in 1,000 babies. In about two thirds of affected babies they appear on the face. A port wine stain usually becomes darker and thicker with age and, having been flat, may develop surface lumps. These birthmarks can occur due to lack of smooth muscle lining around thin-walled blood vessels (capillaries), or they can be due to lack of nerve fibres which usually supply the blood vessels.

Should I see my GP? In the first instance, you should see your GP or talk to the paediatrician who checked your baby in hospital. The doctor may then refer your child to a specialist birthmark unit.

What treatment is available? For children with port wine stains, laser treatment can produce a significant lightening in colour for the majority or in some cases you get near complete clearance.