As always, SmartPractice is dedicated to giving you easier access to educational resources and training so that you can give patients the diagnosis they deserve. To help answer some common clinical questions, we sat down with the Contact Dermatitis Institute’s Medical Director to help give some clarity.

Dr. Dathan Hamann, Contact Dermatitis Institute’s Medical Director

Can I patch test with cosmetics?

Yes! Any leave on products can be placed in a chamber as is and tested. You can also test with topical steroids, emollients, barrier creams and massage oils. Testing with products that are liquid and then become a solid is also okay: mascara, nail polish and perfume can all be patch tested with as is.

Do you recommend testing a patient’s laundry detergent? 

I generally do not test laundry detergent. I don’t think it’s dangerous and a 1:100 dilution would be very reasonable, but I find that the reactions are difficult to interpret as they often have very high pH. It is also difficult to know how concentrated these detergents are. I’m not aware of any ongoing concern about new or undeclared allergens in detergents that we fail to detect by standard/extended patch test allergens.

We have several patients who bring in essential oils to be tested.  In the past, we have placed one drop of the oil on a paper Finn chamber, which has yielded results of blisters and sometimes even pus. Is there a better way to test these oils?  Should we not occlude them in a chamber?

I strongly recommend testing patients with their own essential oils. There is a clear body of literature that essential oil allergy may not be detected with our current standard fragrance markers in the ACDS/NACDG series (see citation below). I always warn patients that essential oils are not standardized and have a higher chance of extreme reactions, scarring, etc. You’re not doing anything wrong. This is common. Tell patients ahead of time. Extreme reactions can be difficult to interpret and can even be both irritant and allergic together. In general, the swelling/induration will worsen after removal for true allergic reactions. Ignore crusting/scabbing for the final read. Focus on swelling. For very irritating essential oils, you can perform “semi-open” testing where you apply the oils to the skin in a grid-like pattern and then cover loosely with gauze so there isn’t cross contamination, but also no occlusion. It’s less irritating. You can also perform a repeat open application test (ROAT) where you instruct the patient to apply one of their oils to the antecubital fossa daily for 1-2 weeks. This may be done serially over time for patients with multiple products. Eczematous eruptions are generally allergic. Many of these patients may have concomitant ACD/ICD. Many of these patients improve with essential oil avoidance.

How do you patch test with clothes and shoes?

I highly recommend patch testing with pieces of patients’ clothing and shoes. Cut a 1-inch x 1-inch square and get it wet, then tape it to the back with the other allergens and leave it on for two days. If it is positive, it is generally due to a dye, but may also be from formaldehyde or residual detergent. You also can use this method with any non-latex gloves (for gloves, you do not need to get the 1-inch x 1-inch piece wet).