In some cases, people are allergic to chia seeds and consuming them can cause hives, rashes or watery eyes, according to Heal With Food. In rare cases, some people have a severe reaction to chia seeds that causes trouble breathing and swelling of the tongue. This allergy is associated with a mustard allergy. People who are allergic to mustard or other plants in that family should avoid chia seeds. In other people, chia seeds cause gastrointestinal distress due to their high fiber content.
According to WebMD, the high level of alpha-linolenic acid contained in chia seeds has shown an increased risk for the development of prostate cancer in studies. People with an increased risk of prostate cancer should avoid consuming chia seeds. Because there is little research done on the health effects of eating chia while pregnant or breast-feeding, it is recommended to avoid consumption of chia seeds while pregnant or breast-feeding to prevent possible negative effects.