Some common causes for a scratch on the skin are a self-inflicted scratch, a light skin injury or an animal's claws. Another cause may be a skin condition called dermatographia, notes Mayo Clinic.
Most scratches to the skin occur through events such as a skin abrasion due to a fall on pavement. A pet can also cause these marks. These scratches usually heal without incident and may require only a topical ointment, states Healthline.
Scratches can also develop with the condition dermatographia. This can occur when someone scratches his or her skin and the skin becomes irritated. The skin can become red and a raised welt may form. Although the exact cause for this medical issue is not entirely known, it may be related to factors such as allergic reaction or taking certain medicines, notes Mayo Clinic. Because the symptoms usually resolve on their own within 30 to 40 minutes, there is no treatment required for dermatographia.