If you think your skin is reacting to a certain substance and you go to see a doctor, they might recommend a test called a patch test. But what exactly is this, and what will happen when you go for it? In this post, we're going to cover what a patch test is, what will be tested, what will happen when you go for your patch test, as well as what the results mean and possible side effects that you can develop from the patch test itself.

Let's start off by briefly covering what patch testing is. Patch testing is a special procedure that's carried out in dermatology departments to find out whether your skin condition is caused or potentially made worse by an allergy to substances that have come into contact with your skin. This is called a contact allergy. Substances that cause an allergic reaction are called allergens, and they may be found both at home and at work—things like the metal buckle on your belt, hand washes, or even cat or dog hair.

So, you've been referred for the patch test, but what exactly will be tested? Many thousands of substances can cause a reaction, but the most common 40 or so, which deliberately or by accident may come into contact with the skin, include things such as rubber, chemicals, preservatives, metals, perfumes, cosmetics, and plants. Additional substances are often added to this list if it's thought they may be causing your particular skin condition. You may also be tested with items you come into contact with at home, at work, or socially, such as personal toiletries.

What should you bring to the patch test clinic? When you're sent your appointment for the patch test at the hospital, they should also give you some instructions on what you need to bring. But if they don't, try to remember a list of all your medications, as well as all ointments and creams that you use. This includes both prescribed medications, creams, and ointments as well as those that you might have bought yourself over the counter. It's also worth bringing the items you use at home which could be causing or worsening your skin condition—things like toiletries, cosmetics, perfumes, nail, and hair products. If you put any products directly on your skin, then try to bring both the product and the packaging where the ingredients are listed. For other items such as household cleansers, washing powders, and fabric softeners, it's usually only necessary to bring the packaging that shows the list of ingredients.

If you've been asked to bring any particular products or substances, it's important to remember to bring them with you to all three appointments that you're going to need to attend. And I'll explain why there are three appointments just later on in this post. On the other hand, if you think that substances at work might be making your skin condition worse, then try to remember to bring in the health and safety data sheets (sometimes called the C sheets) of these products. These will be available at your place of work, but you might need to ask the health and safety officer in advance to provide them. You may be asked to bring samples of these products for testing if necessary.

Now you know what you need to bring with you, but what does patch testing actually involve? You'll need to attend the hospital for three visits during a one-week period. On the first visit, each substance to be tested will be applied to your back in special small disk containers that are held in place by hypoallergenic tape. The location of the containers is identified by marking your back with ink. Occasionally, the arms or your thighs might also be used to do the patch test. Itching of the test areas is quite normal, but you're advised not to scratch. You should allow up to two hours for the first visit. The substances will remain taped in place for 48 hours or until your second visit. It's at this second visit that any potential reactions could be noted. Additional patches are sometimes added at this second visit. The marking ink and tape need to remain on your back for at least a further two days.

If you're being tested for a potential reaction to sunlight, then it might be necessary to expose part of your arm or back to ultraviolet light at this second visit. This is called photo patch testing. Finally, on the third visit, the skin of your back will be checked, and if there are any reactions, these will be discussed with you.

It's possible that your patch tests will be negative, meaning that your skin didn't react to the substances being tested. This usually means that a contact allergy will be less likely to be the cause of your skin problem, and the doctor may wish to investigate other causes that could be causing your skin reaction. It's also worth noting that your doctor may decide not to patch test. This is especially the case if you're pregnant, breastfeeding, have extensive eczema on your back or other skin disease, have used a sunbed or been sunbathing in the previous six weeks, are taking a moderate or high dose of steroids, have applied steroid ointments or creams to the back within 72 hours, or are taking other drugs that suppress the immune system. If you're not sure if any of these apply to you or whether the test will go ahead, then just call the clinic a few days before the test to check if it will still go ahead.

So now we know what will happen in a patch test, but what does a positive patch test look like? A reaction will typically be red or pink or look darker than the normal skin, as well as itchy, and there's often a raised area at the site where the substance was applied that you've reacted to. This usually disappears after a few days. A strongly positive patch test can sometimes cause a local blister, which may last for several weeks. It's also worth mentioning that a reaction can occasionally occur after the third appointment. If you do develop a late reaction after the third appointment, please take photographs and contact your clinic.

A couple of other important points are that you shouldn't apply ointment or cream to your back on the morning of the test and try to avoid getting your back wet the week of these tests. It's also important not to expose your back to the sun or sunbeds during testing and to try to avoid sports and heavy physical work during the week of the tests. This is because if you sweat, the patches could fall off.

Some of my top tips would be to wear an old bra or shirt for the week of the tests. Wearing a shirt or vest to sleep in can protect the patches. Clothes that open at the front can be easier to take on and off compared to those which need to go on over your head, and this can again avoid the patches from being knocked off. If a patch starts to peel off, then tape the edges down using the tape that you should have been given in the clinic. But if a whole patch comes loose, remove it, note the time and date that it came off, and take a photo of the area to bring to the clinic. If you've got any concerns or questions, you can always give the clinic a call.

Finally, what side effects can occur? Side effects to the patch test itself are rare, but they can include the following: First, you might notice that if your skin does react to one of the substances being tested, the reactions might remain for a few weeks before they fade away. This means the skin could be raised, red, or irritated, but as mentioned, this should settle down within a few weeks. If you've got pre-existing eczema, then a positive patch test may be accompanied by a temporary flare-up of your eczema. Some people also mention that they've noticed an increase or decrease in their skin color, which might be seen at the place where the patches were. Again, this may last for several months. Finally, two very rare side effects are scarring of the skin, and you may become allergic to one of the substances that was applied during patch testing. If this happens, you'll be advised to avoid the substance moving forward.

I hope you found this post helpful and informative. For more information on patch testing, please do check out the links in the description box of the video. If you're looking to scale your medical brand on YouTube or are interested in sponsoring our videos with your products, feel free to book a consultation with us.