In areas that are shaded, for example in oak woodlands or coastal redwoods, poison oak grows as a taller, climbing vine that supports itself on other forms of vegetation or upright objects through aerial roots. The leaves on poison oak consist of three leaflets with the stalk of the central leaflet longer than the other two. On occasion there may be five, seven, or even nine leaflets. Leaves on true oaks, which are similar, grow single and not in groups. Poison oak leaves alternate on the stem, with leaflets that are one to four inches in length and are smooth with toothed or lobed edges.
The surface of poison oak leaves may be either dull or glossy; at times they can even be hairy, particularly on their lower surfaces. During the spring, poison oak produces small, white-green flowers where the leaves attach to the stems. White-green and round fruit form late in the summer. Late spring and summer finds the leaves on poison oak a glossy green in color, later turning shades of red and orange. Poison oak can be found in large growths in areas where established vegetation has been disturbed, especially along the sides of roads, in abandoned land, or in uncultivated fields.
The main concern with poison oak is the allergic reaction it causes in many people. Every member of the genus, 'toxicodendron,' to include poison oak, poison sumac, and poison ivy, can cause allergic contact dermatitis. Approximately two-million people experience skin poisoning every year in America, mainly because of these three plants. In the state of California, the number of work hours lost due to dermatitis caused by poison oak makes it the most hazardous plant in the entire state.
People whose skin comes in contact with poison oak leaves or stems at any time during the year can experience an allergic reaction. When the allergen contacts a person's skin, the allergen is quickly absorbed into the person's skin and the surrounding cells. Within a period of one to six days, the person will experience itching and skin irritation, followed by water blisters that may exude serum. Fortunately, the serum excreted from these blisters cannot be transmitted to other areas of a person's body, or to other people. The dermatitis very rarely lasts for longer than ten days.
Around half of the population is sensitive to poison oak and poison ivy. Approximately seventy-five to eighty-five percent of people who are sensitive to poison oak and poison ivy have the potential to develop an allergy to them if they are exposed to a sufficiently high concentration of the toxin. Once a person has experienced a reaction to the toxin, their body responds with a cell-mediated immunity, which is a delayed hypersensitivity. People who have developed delayed hypersensitivity are sensitive to the toxin; repeated exposure to it increases their sensitivity to the toxin. Long periods without exposure to the toxin reduces a person's susceptibility to the allergen.
There is no known difference in sensitivity to poison oak based on a person's gender or race. Animals do not usually experience skin irritation from contact with poison oak because they are protected by fur. Dogs might contact poison oak on either their underbellies or their noses. Other than direct contact with poison oak, the allergen can be transmitted from other sources such as contact with gloves, clothing, tools, or pets who have had contact with it. When poison oak is burned the oils can be transported through smoke particles. People who breath the smoke particles can experience a severe respiratory irritation.
Once a person has come in contact with the allergen, the best way to avoid skin irritation is to pour a mild solvent like rubbing alcohol over the area of their skin that has been exposed, then follow it with plenty of cold water. Warm water would only enhance the penetrating ability of the allergen. If rubbing alcohol isn't available, wash the affected area with a lot of cold water. It is important to wash within five minutes of the time of exposure to prevent a rash. Even if it is too late to prevent a rash, wash the affected area to remove excess plant oil in order to keep the rash from spreading. The toxin in poison oak is an oil and will not dissolve in water. Large enough amounts of water will; however, dilute the oil to the point where it isn't harmful.
Use of only a small amount of water, or using disposable hand wipes, will probably spread the toxin instead of removing it. Soap can be used to wash but only of it is used with large amounts of water - otherwise it will spread the toxin as well. It is also important to remember that washing with rubbing alcohol or soap after being exposed to poison oak will remove the protective oils from a person's skin too. Remember to thoroughly was your hands because they are a major way to transfer the toxic oil from poison oak to additional areas of your body.