What is leaky gut or leaky gut syndrome? According to Dr. Weil, Leaky Gut Syndrome, “is the result of damage to the intestinal lining, making it less able to protect the internal environment as well as to filter needed nutrients and other biological substances. As a consequence, some bacteria and their toxins, incompletely digested proteins and fats, and waste not normally absorbed may 'leak' out of the intestines into the blood stream. This triggers an autoimmune reaction, which can lead to gastrointestinal problems such as abdominal bloating, excessive gas and cramps, fatigue, food sensitivities, joint pain, skin rashes, and autoimmunity…Leaky gut syndrome may trigger or worsen such disorders as Crohn's disease, celiac disease, rheumatoid arthritis, and asthma.” 
Much of my research has resulted in my belief that leaky gut can lead to food allergies (and contribute to autism). As we know, food allergies are an immune system response to food proteins. The most commend food proteins that cause food allergies are dairy, egg, soy, wheat, egg, tree nuts, peanuts, fish and shell fish. It is my understanding that when a child is exposed to one (or more) of these allergens, a food allergy can be triggered especially if that child had leaky gut syndrome. While most doctors do not test for leaky gut syndrome and because it is invisible to the eye, a parent must rely on symptoms. As Dr. Weil states, rashes are a symptom and you can see a rash on your child. Other symptoms may be hard to identify because children cannot effectively communicate how they feel. An infant can’t tell you that he or she has gas, cramps, pain or trouble breathing. But a skin rash is obvious and can be the offending protein making its way out of the body through the skin. My first son had cradle cap and skin rashes on his arms, legs and occasionally his back and face.
Another symptom can be thrush or candida overgrowth--more commonly known as yeast. While a 'yeast infection' is something women ususally think about with respect to reproductive health, it can equally affect the digestive track. The National Candida Center explains, “Candida overgrowth (candida albicans) can lead to candida yeast infection and leaky gut syndrome which is medically referred to as intestinal permeability. Leaky gut is a major gastrointestinal disorder that occurs when openings develop in the gut wall. These tiny holes can be created when candida overgrowth moves to a more serious stage of candida yeast infection and the candida yeast grows roots or hypha (plural hyphae) which is a long, branching filamentous cell of a fungus. This fungal growth is a more advanced stage of development in the candida albicans yeast infection. The hyphae spreads the bowel wall cells apart so that acidic, harmful microorganisms and macromolecules are then able to pass through (leak) these openings and enter the circulatory system. Thus the name 'leaky gut.' The body is alerted to the invader and creates antibodies for protection, activates the immune system, and thus is born a food allergy. Food allergies are directly linked to leaky gut and candida yeast infection overgrowth.” 
For years, my first son had a lot of white stuff on his tongue. We’d try to brush it off and use mouthwash, but it would reappear. Our current doctor identified it as candida. After one and one-half years on a probiotic regimen prescribed by our doctor and careful rinsing of toothbrushes with a hydrogen peroxide-based mouthwash, my son's tongue is finally a beautiful pink. It is my hope that if his intestines are now healed from a candida overgrowth then perhaps his body will outgrow his dairy and egg allergy. He just turned eight years old this past January and while he has made progress in his reaction severity over the past seven years, the allergy still exists (mild to moderate according to the skin prick test results). While I have no proof as to the cause of the candida problem, it is my opinion that too many antibiotics during infancy and toddler years without replenishment of probiotics, set him up for food allergies. In fact, I remember that when he was six months old, he had his first round of antibiotics. Around that time, I tried to wean him from breast milk to cow’s milk-based formula--thus producing our first allergic reaction.
If I had to do it over again, and know what I know now, I’d find a doctor who used antibiotics sparingly and who would have recommended a probiotics supplement for my child, especially after the use of antibiotics. Ironically, the use of probiotics can also help fight off illness and boost the immune system as well--so the need for antibiotics is reduced.
 Weil, M.D., Andrew, "What is Leady Gut?" http://www.drweil.com/drw/u/QAA361058/what-is-leaky-gut.html, Weil Lifestyle, LLC.
 "Candida Yeast Infection Leaky Gut, Irritable Bowel and Food Allergies," http://www.nationalcandidacenter.com/leaky-gut/, National Candida Center.