What are brown birth marks?

Answer 1

They are little beauty spots or moles and it is just part of your skin. Sometimes it fades around the time you get 14 but otherwise it just stays attached to you. If it is big or itchy visit a skin cancer place to have it checked out.

All of the above is true, but, IMO, there's a bit more to add:

Brown birthmarks are concentrations of melanocytes in the skin - ie areas where there are higher than average levels of skin pigmentation (melanin) causing a brown mark.

They vary in size from small (commonly called "moles") to large (generally classified as any mark more than 1.5cm across); may be smooth & regularly shaped (typically round or oval), or irregularly shaped (often called "cafe au lait" marks), & some may be raised above the skin surface and/ or have a rough surface. Some brown birthmarks have hairs growing from them, and some may have constellations of darker "freckles" within the lighter mark.

Most people have some moles (often they appear at ages 5-7, or later at puberty, & therefore not strictly speaking "birthmarks"): brown birthmarks - brown naevi present at birth, & usually a bit larger than moles - occur in approximately 5-10% of many human populations.

It's not certain exactly why people have such birthmarks, but clearly some genetic factors are at work: it's not uncommon for members of one family to have similar marks on the same areas of their bodies, but equally such marks are just as likely to occur apparently randomly in individuals.

Most brown birthmarks are located on the trunk, buttocks & legs. They occur more frequently in women than men, although the "Becker's naevus" (a large, usually hairy, brown mark typically occurring on the chest or shoulders/ upper back) is a "male birthmark" which, in fact, appears after puberty, probably triggered by testosterone production. Black people often have brown birthmarks, but they're less noticeable due to the darker skin. Among white people they occur fairly commonly on blondes, and most frequently redheads. East Asians very rarely have such marks; their birthmarks tend to be black/ purple or bluey/ grey.

With some exceptions, brown birthmarks are harmless: if very large or unfortunately located, they may cause cosmetic/ psychological problems, but generally such marks have no adverse health implications. The exceptions include multiple "cafe au lait" marks on one person, which may be an indicator of certain neurological conditions, and any mole/ birthmark that starts to show changes (in, for example, colour, size, shape etc, or which itches or bleeds): any changes in a mole/ birthmark should be examined by a doctor as this may indicate malignancy.

To summarise, brown birthmarks are common, & are simply unusually high concentrations of melanocytes in an area of skin, probably caused by minor genetic anomalies. Some are hereditary, but most are probably not. Most are totally harmless, but if cosmetically problematic may be surgically removed; although in some cases the excision scar may be as unsightly as the mark. Any change in a mark should be medically examined immediately, but it's important to appreciate that most brown birthmarks are no big deal - simply part of the normal range of human bodily variations.