Patient own samples and dilutions
When patch testing, it is recommended that patients are tested to their own product samples, in addition to commercially available allergens. Approximately 10% of additional cases of ACD will be detected by testing with patients’ own samples.
Patch testing with patients’ own products is recommended because:
- It helps to confirm the causative allergen and testing with own samples may assist to prove causality in medicolegal cases
- Sometimes testing to patients’ own samples is the only diagnostic clue which leads to the identification of the cause of the contact dermatitis
- Testing own products also assists in detecting rare or new emerging allergens, and also reflects actual exposures in the workplace
- Sometimes a patient may not react to individual ingredients, but may react to a complete product. This is known as compound allergy
Work undertaken by the Occupational Dermatology Research and Education Centre (ODREC) has suggested that people working in some industries significantly benefit from being patch tested to their own samples. These include people working as machine operators, tradesmen and health care workers.
The practical aspects of testing patients’ own products
As part of the patch testing process, patients are asked to bring in products that they are using from work and home. These products may include shampoos, makeup, hand washes, gloves, moisturisers and hair dye, along with work chemicals such as epoxy resins.
Many products need to be diluted, as they are too strong to be tested directly on the skin, and would cause an irritant reaction. This is not a true allergic reaction, and should not be mistaken for one. They may be too acidic, too alkaline, or too concentrated.
The general principle for determining when a product should be diluted is:
- If it is usually mixed with water and only stays on the skin for a short period of time, and then rinsed off, then it should be diluted e.g. hand wash.
- If it is used directly on the skin and is left on, such as a moisturising cream, it will not need to be diluted.
- If it is a strong chemical. Chemicals should be diluted to the appropriate concentration for patch testing. For example, epoxy resins are usually tested at 1%. If an epoxy resin is present at a concentration of 25%, then that substance is diluted 1 in 25.
Products that are usually diluted include:
- Shampoos and conditioners
- Hand cleansers and liquid soaps
- Facial cleansers
- Hair dye
- Work chemicals (remember not all can be tested, please read below)
The doctor will order the required dilution for each product on the patient’s patch test chart. Some of the more common dilutions can be found in the Dilutions information sheet or in PatchCams©.
Figure 1 – What you need when diluting patient products
| Figure 1 depicts the equipment required when diluting patient samples, which includes:
|
How to dilute samples
For dilution of water or liquids, draw up the required volume of water with an insulin syringe, place in a pill cup and then mix with the required amount of product (use wooden stick applicator) and dab the diluted mixture onto the patch. Dilutions are made as per Table 1.
Common dilutions when using 1ml syringe of water:
1% dilution – a small dot of sample (i.e. one match head size dot) mixed with 1 ml water
10% dilution – about 2 dots of product sample (i.e. 2 match head size dots) mixed with 1ml water
If you need a smaller dilution such as 0.1% or 0.01%, serial dilutions can be made.
For oil-based products you will need to use soft white paraffin/Vaseline/petrolatum jelly for dilution instead of water. Use a 10 ml syringe packed with petrolatum, and dispense the volume (mL) required into a mixing cup. Mix well and apply to the patch.
For example, use 1 ml of petrolatum from the syringe, and 2 match stick head size samples of product for a 10% dilution, or only one tiny match stick head size for 1% dilution. Some people may prefer to use a 10 ml syringe for the dilutions.
Table 1 – Dilutions for Patch Testing (Adapted from ?
Desired percentage dilution (%) | Quantity (µl) to be mixed in 10ml of vehicle |
0.1 | 10 |
0.5 | 50 |
1.0 | 100 |
2.0 | 200 |
5.0 | 500 (0.5ml) |
10 | 1000 (1.0ml) |
The doctor will order the required dilution on the patient’s patch test chart. A few common dilutions are:
- Shampoo and conditioner diluted to 1% in water (1 ml water, and one match head size of shampoo or conditioner)
- Hand cleansers, liquid soaps, body washes 10% in water (1 ml water and approx. 2 match head size drops of hand cleanser)
- Hair dye 10% in petrolatum (1 ml of petrolatum dispensed from 10ml syringe of petrolatum, mixed with 2 match head size of hair dye).
Dilutions chart – A guide
See the Dilutions information sheet or refer to PatchCams© for the most common dilutions. If you are unsure about what the product is and how it should be diluted, please refer to the following incredible resource.
Anton De Groot’s book: Test Concentrations & Vehicles for 4750 Chemicals.
There were 4 editions of this book which may be available to purchase online second hand. The 5th edition has been published online and can be accessed by members of the European Society of Contact Dermatitis (www.escd.org) or member of the American Contact Dermatitis Society (www.contactderm.org).
When patch testing patients own products, it is important to be aware that one item can have several components, for example a glove can have a material and rubber component, while a shoe can have tongue, fabric inner, sole and outer sole. Test each part by applying each to a separate patch (using petrolatum to stick to dics) and label on the chart. Table 2 demonstrates how to patch test different patient samples “as is”.
| For all patient own products, if you don’t know what it is then don’t test it. |
Things that should not be tested:
- Fuel/diesel
- Strong cleaning products e.g. toilet cleaner. They often have ingredients called quaternary ammonium derivatives which are very irritating and not allergens.
- Cement/concrete
- Antifreeze
- Car or floor wax
- Organic solvents
- Metal chips (coarse)
- Rust remover
Many things are irritants and should not be tested. If you don’t have information on the product or are unsure of what the product is – do not test it! Refer to De Groot for more details.
Table 2 – Examples of testing patient samples
 | Examples of removing rubber from hammer handle using a blade. Stick on to patch using petrolatum |
 | Example of removing outer surface of a face mask Stick on to patch using petrolatum |
 | Example of blading a wood sample. Stick on to patch using petrolatum. |
 | Spray perfume into a cup and use a stick to apply to patch |
 | Example of glove sample being chopped and applied to patch. Ensure it is the same size, or slightly smaller than the size of the disc |
Videos to watch:
