Contact dermatitis is another kind of allergy, one that appears as a skin rash. One of the most common triggers of contact dermatitis in the great outdoors is poison ivy. The resin of the plant contains an oily substance called urushiol that's easily released and spread when the leaves are crushed or rubbed. There's usually no reaction the first time you're exposed, but watch out! About 85% of people will eventually develop an allergic reaction to poison ivy after being exposed to it several times. Within 12 to 40 hours of brushing against this innocent-looking shrub, susceptible people will typically develop an itchy rash, starting as reddened skin, leading to bumps and blisters. After a few days, the blisters break and the oozing sores begin to crust over and heal.

Your best defense is to avoid contact with poison ivy plants. Learn to recognize them by their slightly glossy green leaves growing in groups of three - but their shape can vary. If you're in heavily wooded areas and it's impossible to avoid them, wear long sleeves, long pants, and gloves. Remember, the oils can cling to your family pet's fur, so be careful when handling your pet after spending time in wooded areas - a bath may be necessary.

What if you're unlucky enough to get some urushiol on you? First, try to wash it off right away. Even a running stream will do, but soap and water is best to keep the oil - and the rash - from spreading. The rash will usually go away on its own in a few days, but it can be uncomfortable in the meantime. Wet cold compresses can soothe the rash, while calamine lotion, witch hazel, or Burow's solution helps dry it out. Oral antihistamines can also be helpful in controlling itchiness. See a doctor if the rash is severe, is on the face or genitals, or covers more than 20% of the body. Prescription medications, such as antihistamines and corticosteroids, can help in such cases.