Definition: Seborrheic keratosis is one of the most common types of noncancerous (benign) skin growths in older adults. In fact, most people develop at least one seborrheic keratosis at some point in their lives. 
Other names: Barnacles 
A seborrheic keratosis usually appears as a brown, black or pale growth on the face, chest, shoulders or back. However, a seborrheic keratosis can occur almost anywhere on the body. The growth has a waxy, scaly, slightly elevated appearance that distinguishes it from a mole. Occasionally, it appears singly, but multiple growths are more common. A seborrheic keratosis is also usually round or oval shaped and range in size from very small to more than 1 inch (2.5 centimeters) across. 
A seborrheic keratosis has a characteristic “pasted on” look. They are classically described as looking like someone took clay or a blob of dirt and “stuck” it on the skin. The edge of the seborrheic keratosis is not attached to the underlying skin making it appear that it could be removed by picking it off with your fingernail. This is because seborrheic keratoses arise from the epidermis, or top layer of skin. They don’t extend deep into the skin like warts. 
There are two different appearances of a seborrheic keratosis; a flat (smooth surface) or slightly elevated with a warty surface.
Warty surface – Seborrheic keratoses may look like warts but they don’t contain human papilloma viruses that cause warts. As they develop some can have a very rough surface with deep pits and fissures almost like cauliflower being pulled apart. 
Smooth surface with horn pearls – Some seborrheic keratoses don’t have a rough surface. If they are smooth, they contain tiny bumps that look like seeds that are lighter or darker than the surrounding tissue. These are called horn pearls and they are actually bits of keratin that develop in a whirling, circular pattern. Sometimes these horn pearls are best seen with a magnifying glass. 
Seborrheic keratoses tend to itch especially in older people. Some people will unintentionally manipulate or “pick at” a seborrheic keratosis and cause it to be further irritated and itch more. If irritated enough, the skin around it can become red and the seborrheic keratosis itself can bleed. 
Seborrheic keratoses are move common in people over age 50 and those who have this condition in their families, suggesting a genetic component. 
The first and usually the best choice is to leave them alone. They may get larger, but they are not precancerous so leaving them there for the life of your skin is not a problem. Seborrheic keratoses are usually removed because they itch, they interfere with clothing or jewelry, or they are cosmetically unacceptable.
Removing Seborrheic Keratosis
If you decide to have a seborrheic keratosis removed, there are several ways to do this. A few of the most common are listed here.
Keep in mind that most insurance companies and Medicare won’t pay for the removal of seborrheic keratoses if done only for cosmetic reasons. Medical reasons for seborrheic keratosis treatment include intense itching, pain, inflammation, bleeding and infection. 
When to see a Doctor
Sometimes seborrheic keratoses can be very difficult to distinguish from melanoma. Especially when they first appear, they can have several of the characteristics of atypical growths including irregular borders and color variation throughout the lesion. You should not hesitate to see your doctor about any skin rashes or bumps that concern you. 
1. Seborrheic keratosis. http://dermatology.about.com/cs/benignlesions/a/sebk.htm