Patch Testing for Skin Allergies

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A patch test is a skin test used to find the cause of a possible allergic reaction on the skin. This reaction is called allergic contact dermatitis. Contact dermatitis is a reaction to something that came into contact with the skin. This kind of allergic reaction usually causes inflammation (redness, itching). 

Patch testing is done by the dermatology clinic. During patch testing, different substances are placed on the skin and taped in place. The patches are typically placed on the back, left on for 2 days and then removed. The area of skin that was tested will be evaluated by the dermatologist 2 to 4 days after the patches are removed. 

You will need to bring your child to the dermatology clinic 2 to 3 times during the week that the patch testing is done. Generally the test week is a total of 5 days.

It is important to follow the guidelines below to get accurate results. Patch testing evaluates a slow, delayed skin reaction so it is important that the patches stay in place. The test site must also be protected throughout the entire test week. 

Preparation for the Test 

Getting the skin ready for your patch test is important. Following these instructions will help you to get more accurate, reliable results. 

  • Avoid sun exposure for 1 to 2 weeks before patch testing. 

  • Do not use topical medicines (creams and ointments) on the back and any other area where patches may be placed for at least 1 week before patch testing. You can continue to use these medicines on areas of the body where patches will not be placed. 

  • You may use moisturizers on the skin until the day before patch testing. 

  • Your child may continue to take any prescribed antihistamines as usual before and during the testing.

 During the Test Week 

Parents may stay with their child before and throughout testing. 

  • The patches and test area marked with ink must be kept dry throughout the entire test. 

  • Do not apply anything to the test area. This includes all soaps, creams, ointments and moisturizers. 

  • Do not scratch, rub, loosen or remove the patches. 

  • Avoid physical activities that will loosen the tape. 

  • Do not expose the test area to sunlight. 

  • Avoid hot areas and activities that cause excessive sweating. 

Continue to take your prescribed antihistamines. 

The patches must be kept dry. Your child should not take a shower or bath. Wash areas of the body where there are no patches with a washcloth or bath sponge. Be careful not to get the patches wet. 

The First Visit: 

The patches are usually placed on your child’s back and left in place for 2 days. 

  • Your child should wear loose, comfortable clothing. 

  • Your child should wear old, dark-colored clothes to avoid stains from the marker. 

Small sheets, or patches, holding different substances are placed on the skin. The nurses will use a marker to outline the edges of the sheets. Then the sheets will be secured with tape or another sticky bandage (dressing). 

The Second Visit: 

The second visit is usually 2 days after the patches were put on. Typically you will bring your child to the clinic to have the patches removed. The nurses will carefully remove the tape and patches. They will re-mark the skin where the patches were. The nurses will check the area to see if the skin shows any signs of a reaction. In many cases a reaction may not have shown up yet. It is still important to come back to the clinic to have the area checked one more time. 

Continue to keep the skin dry where the patches were. Do not let your child take a shower or bathe where the patches were. Do not apply creams, ointments, or moisturizers where the patches were. Do not let your child scratch the skin where the patches were. Your child should avoid hot areas and activities that cause excessive sweating. 

Removing patches: Normally you should not remove patches yourself. Usually the nurses in the dermatology clinic remove them. Occasionally the doctor will ask a family to remove the patches at home. If you have been given this instruction you will remove the tape and clear bandage carefully. You will re-mark the borders of the patch testing sheets with the marker you were given before you take them off the skin. 

Sometimes a patch may fall off or pull away so that it is not actually touching the skin. If this happens it is important to let your child’s doctor know at your next appointment. 

The Third Visit: 

The third visit is usually 4 to 5 days after the patches were put on. Your child will come to the clinic to have the skin checked. It is important to check the skin again to look for skin reactions. The nurses and doctor will look at the child’s skin and tell you if there are any substances that your child should avoid. 

After your child’s visit you can restart topical creams, ointments, and moisturizers. Your child may shower and bathe normally. 

If you have any questions, be sure to ask your child’s doctor or nurse.

Patch Testing for Skin Allergies (PDF)

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