Back to Sexual health. If you don't wash underneath the foreskin correctly, a cheesy-looking substance called smegma may begin to gather. Smegma is a natural lubricant that keeps the penis moist. It's found on the head of the penis and under the foreskin. If smegma builds up in the foreskin, it can start to smell, stop you easily pulling your foreskin back, and become a breeding ground for bacteria. This can cause redness and swelling of the head of your penis, called balanitis.

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Topic Overview
Smegma is a substance made up of oil and dead skin cells. It can accumulate under the foreskin in uncircumcised males or around the folds of the labia in females. Left untreated, smegma can cause an odor or in some cases, harden and lead to irritation in the genitals. Read on to learn how to get rid of and prevent smegma buildup. The simplest way to remove smegma is to adjust your personal hygiene routine. In men, that means properly cleaning your genitals , including around and under your foreskin. Your body produces a lubricant to help the foreskin retract.
When to call the doctor
In the first several years your son's foreskin will separate from the tip of the penis. Some foreskins separate soon after birth or even before birth, but this is rare. When it happens is different for every child. It may take a few weeks, months, or years. Once this happens, the foreskin can be pulled back away from the tip of the penis. This is called foreskin retraction. Most boys will be able to retract their foreskins by the time they are 5 years old, yet others will not be able to until the teen years. As a boy becomes more aware of his body, he will most likely discover how to retract his own foreskin. But foreskin retraction should never be forced.
Men who are uncircumcised must take special care of the foreskin, the loose skin that covers the tip of the penis. A man should wash his penis with warm water every day. While washing, he should gently pull back the foreskin and rinse the glans head of the penis and inside the foreskin. When finished, he can pull the foreskin back to its original position. He should also wash the base the penis and the testicles.