Molluscum contagiosum is caused by a poxvirus called the molluscum contagiosum virus (MCV). It infects only the outer layer of skin, producing small, firm, dome-shaped bumps with a characteristic dimple in the center. The virus spreads through direct skin contact, shared objects, and sexual contact, and it can take anywhere from one week to six months after exposure before bumps appear.
The Virus Behind the Bumps
The molluscum contagiosum virus belongs to the poxvirus family, the same group that includes smallpox and cowpox. Unlike those viruses, MCV only infects humans and only targets skin cells. It cannot spread to internal organs or travel through the bloodstream. The virus enters the top layer of skin and replicates inside skin cells, causing them to grow abnormally and form the painless, pearly bumps that define the infection.
Each bump is essentially a small pocket of virus-filled skin cells. The waxy, white core you might notice if a bump is squeezed or broken open is packed with viral particles, which is why touching or breaking the bumps is a primary way the infection spreads to new areas of the body or to other people.
How the Virus Spreads
MCV spreads through three main routes: direct skin-to-skin contact with someone who has active bumps, contact with contaminated objects, and sexual transmission.
- Skin-to-skin contact is the most common route, especially among children who play in close physical contact. Touching, wrestling, or simply brushing against someone’s bumps can transfer the virus.
- Shared objects like towels, clothing, toys, and sports equipment can carry the virus on their surface. This is a frequent path in households and group settings like daycares.
- Sexual contact is a common route in adults, which is why adults often develop bumps on the inner thighs, lower abdomen, and genital area.
- Self-spreading (autoinoculation) happens when you touch, scratch, or shave over your own bumps and then touch another part of your body. This is why a few initial bumps can multiply into clusters over weeks.
The Swimming Pool Question
Parents often wonder whether their child picked up molluscum at the pool. The CDC notes that while some investigations have linked outbreaks to swimming pools, the virus likely spreads through shared equipment rather than through the water itself. Sharing towels, kickboards, goggles, and pool toys creates opportunities for the virus to transfer from one person’s skin to a surface and then to someone else. Thorough disinfection and drying of shared pool equipment reduces the likelihood of transmission.
Why Some People Are More Vulnerable
Not everyone exposed to the virus develops an infection. Your immune system and the condition of your skin both play a role in determining whether MCV takes hold.
People with atopic dermatitis (eczema) face a higher risk. The cracked, inflamed skin that comes with eczema creates entry points the virus can exploit more easily. Children with eczema often develop more widespread bumps and may have a harder time clearing the infection compared to children with intact skin barriers.
A weakened immune system dramatically changes the course of the disease. In people with healthy immune function, molluscum is self-limiting, meaning the body eventually fights it off on its own. In people with HIV or other conditions that suppress the immune system, the infection can become severe and persistent. Bumps may number in the hundreds, grow larger than 10 millimeters (sometimes called “giant molluscum”), and resist treatment. Reduced T-cell counts, impaired natural killer cell function, and a decrease in the immune cells that patrol the skin all contribute to this more aggressive presentation.
The Incubation Period
After the virus enters your skin, it takes time before any bumps appear. The typical incubation period ranges from two to seven weeks, but it can be as short as one week or as long as six months. This long, variable window makes it difficult to pinpoint exactly when or where exposure happened. You may have been infected weeks or months before the first bump shows up, which also means you could unknowingly pass the virus to others during that time if viral particles are present on the skin surface.
How Long the Infection Lasts
In people with healthy immune systems, molluscum bumps typically disappear on their own within 6 to 12 months without any treatment. Some cases, however, can take as long as four years to fully resolve. The timeline depends partly on how many bumps develop and whether new ones keep forming through autoinoculation.
The slow resolution is largely about how the virus interacts with your immune system. MCV has evolved strategies to hide from immune detection within skin cells. Eventually, your body mounts a strong enough inflammatory response to clear the infected cells, which is why some bumps become red and irritated before they disappear. That inflammation is actually a sign your immune system is winning.
Who Gets Molluscum Most Often
Children between the ages of 1 and 10 are the most commonly affected group, largely because of frequent skin-to-skin contact during play and shared items in school and daycare settings. In adults, molluscum is most often seen as a sexually transmitted infection, with bumps appearing in the genital region. Adults with compromised immune systems, whether from HIV, organ transplant medications, or other immunosuppressive therapies, represent the third major group and tend to experience the most persistent and widespread infections.
Warm, humid climates and crowded living conditions also increase the chance of transmission, simply because the virus survives better on moist surfaces and people have more frequent close contact.