What would cause our son to blister very easily after doing sit ups on his lower back and jumping jacks feet?

Blisters are caused by friction or pressure on the skin. In the case of your son, it sounds like the blisters are being caused by the friction of his skin against his clothing or the ground when he is doing sit ups and jumping jacks.

There are a few things that can be done to prevent or reduce the risk of blisters:

- Wear loose-fitting, comfortable clothing made of breathable materials.

- Change your clothes promptly if they become damp.

- Apply a lubricant, such as petroleum jelly or a sports cream, to areas of skin that are prone to blisters, e.g. heels and balls of feet.

- Use padded socks or insoles to reduce friction.

- Take breaks during exercise and avoid overexertion.

If blisters do occur, it is important to treat them promptly to prevent infection. Clean the blisters with soap and water, apply a bandage, and avoid picking or popping them. If the blisters are large, painful, or infected, it is important to seek medical attention.