“Why does my son burst into a sweat whenever he is hungry?”

Sweating is the bodies mechanism created to it dissipate heat so it can cool down. With out sweating it will not be able to dissipate heat and it could over heat that would lead to serious health problems. Some times excessive sweating may not be a normal response to heat dissipation. Even though sweating is a necessary mechanism to cool the body temperature excessive sweating (hyperhidrosis) may cause disturbance in our way of life. hyperhidrosis is therefore a condition where the body parts or the whole body will sweat profusely regardless of the body temperature or the need to dissipate the body heat. Most hyperhidrosis are of unknown cause and are not serious. Some are as a result of medical and hormonal conditions. Exercise, obesity, eating chili, spicy food, kidney disease, over active thyroid gland, adrenal disease, low blood sugar, menopause or other medical conditions are some examples. If your son does not have medical conditions such as diabetes and he is not on any medication, but he is sweating when he is hungry or after prolonger fasting, he likely has low blood sugar (hypoglycemia). Hunger induced low blood sugar or prolonged fasting can cause sweating due to low blood sugar induced adrenalin release. When blood sugar is low or the body perceives that the blood sugar is low it releases adrenalin to release glucose from the body glucose stores so we can get enough energy to support the bodies energy and mainly the brain function. The brain mainly functions on sugar than the rest of the body. So adrenalin is released to allow stored sugar to be used mainly by the brain. Release of adrenalin (fight and Flight) cause sweating palpitation, shakiness, tremors etc. If after adrenalin release the glucose reserve of the body is depleted and we do not eat we may experience stupor, unconsciousness or seizure since there is no sugar to support the brain function.
One can still sweat after prolonged fasting or when hungry in the absence of low blood sugars. The body will perceive low blood sugar before it goes lower and allows the release of adrenalin though blood sugar is normal.
One can also have sugar storage diseases that even with the release of adrenalin the body may not release the glucose properly (storage diseases) to correct the blood sugar. In this case the person need to be seen by a specialist.
Your son may there for responding to adrenalin release most likely due to low blood sugars. You could feed him on time and have him some snacks in between meals. May also consider complex carbohydrate such as corn starch, potatoes etc. to last him longer. It may also be advisable to have him get evaluated properly by his physician.
Good Luck

It could be a sign of hypoglycemia (low blood sugar) or hyperthyroidism.

This may be nothing except an exaggerated response to hunger. However, sweating with hunger could indicate something that needs to be investigated further. I would recommend asking his healthcare provider.

A bit unusual. Could be hypoglycemia - low blood sugar levels - in which case you should talk to your son's physician and have him examined, perhaps also get a home blood glucose meter and check the actual sugar levels at the time that he is hungry and/or sweaty. If the glucose levels are below 60, treat this with 4 oz of orange or other juice and should rise. Then call the doctor to let them know. If all the time he has hungry symptoms and/or such sweatiness, the glucose levels are above 70, then this is not related to low sugar levels.