What is patch testing for?
Patch testing is a way of finding out if you are allergic to anything
that comes into contact with the skin from the outside. This could
include, for example, perfumes, jewellery and plants.
Will patch testing find out all of my allergies?
No. Patch testing detects only the type of allergy that causes itching,
redness, flaking and sometimes tiny blisters from skin contact from
the outside. It does not detect the type of allergy that may come
from diet, or the type that causes sneezing, sinus trouble, asthma or
hives.
How many visits will be required?
Three visits: which must be on a Monday, Wednesday and Friday in
one week. Patch tests are applied on the Monday and removed on
the Wednesday. Results are looked at on the Friday.
Occasionally a 4th visit on the following Monday, may be required.
Unusually, it may not be possible to do the tests when you attend:
for instance, if your skin is very bad or the right materials are not
available.
How are patch tests done?
Substances which are the suspected cause of allergy are stuck
on to your back with sticky tape, which keeps them there for 2 days.
You should wear an old vest and shirt / old bra and blouse on the
Monday and Wednesday visits.
Marks are made on the skin with black ink on the Wednesday visit,
to indicate where the patches were. All the marks and results of the
patch testing normally fade over the weekend. It is rare for red marks
to last a long time.
Please note that the pen used on the skin may mark your
clothing.
During patch testing you will need to keep your back dry, so it is
better to re-arrange certain sporting or social events if you can.
Do not apply any creams or lotions to your back prior to your first
visit.
What are the side effects of patch testing?
There are no dangerous side effects. The patches may be itchy until
they are removed on the Wednesday. Positive patch tests result in a
small area of eczema, the size of a coin, which may be red and itchy
for a few days.
It is rare for patch testing to make you allergic to something that you
were not allergic to before; it is very uncommon for this to happen as
the strength of the patch test solutions is normally too low to cause
allergy; if it does happen, you may develop a positive patch for a few
days or even a week or two after the patch testing is completed. In
this case you should contact the Dermatology Department on 01253
956238 or 957089.
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Author Dermatology Department
Approved by Dermatology Business Meeting
Date Of Publication 14/05/2024
Review Date 01/05/2027
Reference No PL/087 (v9)
