**1.** Some individuals with pollen allergy experience mouth itching and swelling after eating certain *raw* fruits, vegetables and tree nuts. The condition is called [**oral allergy syndrome**][1] or **pollen-food syndrome.**

**2. A certain food allergy as such** may increase intestinal permeability **(leaky gut syndrome)** and allow additional allergens to enter the blood, which can result in multiple food allergies ([PubMed, 2006][2] ; [PubMed, 2016][3]).

**3.** The use of **[antibiotics][4]** in infancy can increase the risk of food allergies alter in life.

**4. [Orofacial granulomatosis][5]** (which may or may not be associated with Crohn's disease) increases the risk for food allergies. A cinnamon- and benzoate-free diet can help ([PubMed, 2006][6]).

**5.** Children with **[inflammatory bowel disease (Crohn's disease or ulcerative colitis)][7]** are at increased risk for food allergies. [Another study][8] has found an association between inflammatory bowel disease and food allergies.

**6. [Infections** or **stress**][9] may increase intestinal permeability and thus induce food allergies in susceptible individuals.

**7. [Cross-reactivity][10]** can cause food allergies: *Alternaria* (a common mold)-spinach syndrome, dust mite-shrimp syndrome, cat-pork syndrome and bird-egg syndrome.

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As a side note, [food protein-induced enterocolitis syndrome (FPIES)][11] can develop in infants after introducing solid foods and can present with multiple food allergies, which, unlike traditional IgE-mediated allergies, do not cause itching, hives, swelling, coughing or wheezing, but "only" gastrointestinal symptoms, such as diarrhea.

  [1]: https://acaai.org/allergies/types/food-allergies/types-food-allergy/oral-allergy-syndrome
  [2]: https://www.ncbi.nlm.nih.gov/pubmed/16880015/
  [3]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5288588/
  [4]: https://medicalsciences.stackexchange.com/questions/18354/is-there-solid-evidence-that-antibiotics-cause-allergies
  [5]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3751572/
  [6]: https://www.ncbi.nlm.nih.gov/pubmed/16775496/
  [7]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4696370/
  [8]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4230978/
  [9]: https://www.ncbi.nlm.nih.gov/pubmed/16292078/
  [10]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4482820/
  [11]: https://www.kidswithfoodallergies.org/page/food-protein-induced-enterocolitis-syndrome-fpies.aspx