My grand daughters skin has started turning red when she is touched , what might cause this she is 17 months old and has not had this problem before

Your : Your granddaughter may have a condition known as dermatographia - an over-sensitivity of the skin that causes red, swollen itchy spots like hives when touched or lightly scratched. No one knows what causes it, though it could be caused by an allergen. In most cases, it doesn't last long and if it uncomfortable, your granddaughter's doctor may recommend treatment with an antihistamine such as Diphenhydramine (benadryl) or Cetirizine (zyrtec). It may also help her to avoid itchy, rough clothing, harsh soaps, and other triggers. Moisturizers can also be helpful.

Poss dermatographism: The cause of dermatographism isn't known, but when the skin is rubbed or scratched it becomes red and may form a welt. The welts usually last 30 minutes or so, but is variable. Generally, using lotions to avoid dry skin and avoiding scratchy fabrics is helpful. Symptoms may include mild itching. Antihistamines like Zyrtec or Benadryl may be helpful. An exam by her doctor can confirm the Dx.