Wikipedia has more on Hippopotomonstrosesquippedaliophobia
Although this may seem silly, there are people who claim from suffering hippopotomonstrosesquippedaliophobia. However, the phobia is not recognized by most doctors. The causes of the phobia are unknown but might stem from difficulties to learn reading back at school, or certain brain patterns. It might be associated to a more worrisome mental illness.
Most of the long words can be found in the medical and chemical vocabulary, such as deoxyribonucleic acid, dichlorodifluoromethane, thyroparathyroidectomized... The longest English word, which has 189,819 letters and takes more than 3 hours to be fully pronounced, is a chemical name. For these reasons, people suffering from hippopotomonstrosesquippedaliophobia should avoid becoming doctors or chemists.