Despite what you may have been told as a child, the claim that swallowed chewing gum remains in your digestive system for seven years is absurd. There is just no scientific evidence to support this claim. No one knows how this myth actually came about, but a fair guess is that concerned mothers created it to discourage their children from eating chewing gum in the first place. If this indeed was the case, it certainly seems to have worked. I have seen several young children thinking twice about eating chewing gum after listening to horror stories about the gum stuck in someone’s stomach causing them appendicitis and what-not. I myself have had several mini panic attacks after accidentally swallowing chewing gum.
Most chewing gums consist of a gum base, sweeteners, flavourings, colourings, softeners and preservatives. The main body of the gum, the gum base, is not digested by us humans as we have no enzymes required for its digestion. Therefore, when gum is swallowed, it usually passes through the digestive tract fully intact, and is excreted at the other end. Often, the excreted gum is easily discernible as it is still the same colour as it was when it was swallowed.
One odd gum-swallow here or there will probably do you no harm, but regularly swallowing gum can have adverse affects. In some extreme cases, swallowed chewing gum can cause severe damage and discomfort. There have been several reported cases of build-ups of chewing gum inside the digestive tracts of people (mostly children) causing them severe constipation and pain. In one case, a four-year-old boy had been suffering from constipation for two years. His parents began offering him chewing gum as an incentive to try to relieve himself (don’t ask me why). He had around six pieces of chewing gum a day, but instead of spitting them out, he swallowed them all. Eventually, the situation became so bad that doctors had to sedate him and surgically remove a mass consisting primarily of gum from his rectum.
Even if swallowing it will do you no harm, you should not eat too much chewing gum in any case. The artificial colours, sweeteners and preservatives in most chewing gums are bad for your teeth and your health in general.
In conclusion, swallowing gum is almost always safe, but for the sake of your health, you should not swallow (or even eat) too much of it.