A six-month-old baby with a hard-on is not necessarily epileptic, but may also be caused by a vitamin deficiency. 1. Epilepsy: can be caused by abnormal brain discharges, usually seizures can be muscle tonus, clonus, disorientation and other symptoms, that is, the so-called “hard to make a hard”, this situation need to go to the hospital for a specific examination, if diagnosed with epilepsy, should be treated as soon as possible. 2. Vitamin deficiencies: the most common are vitamin A and D deficiencies, which may be caused by poor digestion and absorption, unbalanced nutritional intake and insufficient sunlight. In addition to the manifestation of muscle tonus, clonus, and pain, there can also be irritability, irritability, and bone dysplasia and other symptoms. It can be treated by adjusting the diet, regular sun exposure and calcium supplementation. However, timely medical examination is recommended.