Direct skin contact with poison oak results in contact dermatitis. The sap of the poison oak plant contains an oil called urushiol that causes an allergic reaction in humans. The symptoms of an allergic reaction to poison oak is an itchy rash with blisters.
Itching
An allergic reaction to poison oak triggers intense itching. The body's immune system responds to urushiol as an allergen and reacts with a skin irritation. Scratching does not cause the rash to spread but may lead to secondary infections. By scratching the rash, the blisters can open and be susceptible to infection-causing bacteria.
Rash
First time exposure of human skin to urushiol rarely causes an allergic reaction. The Academy of Dermatology points out that repeated contact with poison oak results in sensitivity to urushiol. Citing PoisonOakRash, about 80 percent of all people have an allergic skin reaction to poison oak.
The rash appears once the urushiol has been absorbed by the skin. In most cases, the rash develops within the first hour following contact with poison oak sap. However, the rash may not be evident until one week following exposure. The rash begins as small red bumps anywhere on the body that has been in contact with the oil. The pattern of the rash first appears as a curved line. According to MedlinePlus, the rash can last for 1 to 3 weeks.
Blisters
The red bumps of the rash from poison oak contact can develop into blisters. Referring to Poison Ivy, Oak, and Sumac Information Center, blood vessels in the area of the rash develop gaps that leak fluid and cause blisters. Blisters are small fluid-filled eruptions that can easily break and leak fluid onto the surrounding skin. As the fluid dries, a crust forms over the blister. The fluid in the blisters does not contain urushiol and cannot cause the rash to spread.
