Section 7.1 Diagnosis

Many factors can contribute to a patient’s skin condition. Contact dermatitis may only be one factor. Approximately 47% of patients assessed in our Occupational Dermatology Clinic are found to have more than one diagnosis e.g. irritant contact and allergic contact dermatitis.

Some people may NOT actually be diagnosed with allergic contact dermatitis following patch testing, but it is important to exclude this diagnosis with thorough and appropriate patch testing. For example, young adult patients with endogenous hand eczema (also called pompholyx, dyshidrotic eczema) often experience aggravation from irritants when working in hospitality, but allergic contact dermatitis from hand cleaners or gloves often needs to be excluded.

Differential diagnoses for hand dermatitis for example may include:

  • Irritant contact dermatitis
  • Allergic contact dermatitis
  • Contact urticaria/protein contact dermatitis
  • Endogenous forms of eczema: Hand eczema, atopic eczema, rarely discoid eczema
  • Psoriasis
  • Infection e.g. tinea, bacteria
  • Porphyria cutanea tarda
  • Glove-related hand urticaria

By the end of the patch testing process, all patients should be given a diagnosis of their skin condition, which of course will be partly subjective and partly objective, based on the dermatologist’s assessment. Use of the flow chart “Understanding your skin condition” developed by Associate Professor Rosemary Nixon (see page xx) can help the patient understand their diagnosis (or multiple diagnoses), and how patch testing fits in to the diagnostic journey.

As mentioned, we find it useful to commence the education process at the 48-hour reading, before patch testing and the diagnostic process has been completed, so the patient really understands what is going on. Giving patients initial information about any positive tests after 48 hours helps to engage them in the search for relevant exposure to allergens. We discuss the flow chart with patients again at the conclusion of testing.

Additionally it is important for patients to be aware that late patch test reactions are possible and may occur up to 10 days after testing. It is important to mention this to patients at their final appointment, and to give instructions about what to do if a late reaction occurs. The patient should be advised to phone the clinic and if possible, email a photo of their back. They may need to return to the clinic for the dermatologist to review their reactions.

Remember, general practitioners and other health care professionals may have a limited understanding of delayed hypersensitivity, so it is essential that the patient understands what they have been diagnosed with, the relevance of any positive patch test results and what that means for them on a day-to-day level.

Example cases

Example 1

A young woman presents with axillary dermatitis caused by fragrance in her deodorant, confirmed by a positive patch test reaction to fragrance mix and a positive patch test to her deodorant (tested ‘as is’). She also reacts to nickel, and has a history of having dermatitis some years ago from cheap earrings, likely to have contained nickel. Her reaction to nickel is therefore classified as old or past relevance.


Allergic contact dermatitis to fragrance, current relevance

Contact allergy to nickel, past relevance

It is important to record the fact that the patient reacted to nickel, because she may develop contact dermatitis in the future, such as with wearing a white gold ring, which may contain nickel. However because she does not demonstrate a clinical history of nickel allergic contact dermatitis currently, we classify this as ‘contact allergy”.

Example 2

A nurse with a background of childhood atopic eczema develops steadily worsening hand dermatitis in the context of her work, with improvement on holidays. She usually wears nitrile gloves except with for sterile procedures when she wears powdered latex gloves. She washes her hands with the hospital skin care cleanser. She blames the recently introduced alcohol hand rub. Patch testing reveals a positive reaction to coconut diethanolamide which is present in the hospital skin cleanser. A blood test was positive to latex.


Allergic contact dermatitis to coconut diethanolamide in skin care cleanser.

Latex allergy caused by wearing powdered latex gloves.

Likely contributing irritant contact dermatitis (diagnosed subjectively on history) from wet work. Generally alcohol rubs are associated with less irritant contact dermatitis, because of less water exposure and less use of paper towels.

Background of atopic eczema which means that she is likely to have more easily irritated skin.

In summary

When finalizing a diagnosis for a patient at the conclusion of patch testing, there are a few things to consider. Firstly it is important to list the relevance of each positive patch test reaction: current, old or unknown.

If tests are negative, consider the list of possible causes above. Could the diagnosis be protein contact dermatitis? Do you need to perform prick or blood tests or possibly collaborate with an allergist? Has an allergen been missed or is repeat testing required at a later date?

Patch testing is valuable in making a diagnosis, but it is also important to recognise the possible role of skin irritants and immediate hypersensitivity. People should in most cases, leave their final appointment with a diagnosis of their skin condition. Their skin condition may in fact be atopic eczema, but the patients and their treating practitioners can be reassured that allergic contact dermatitis to their skin care treatments and topical therapy has been excluded on patch testing. To make a diagnosis of allergic contact dermatitis there needs to be a compatible history of dermatitis, a positive patch test and evidence of exposure to that allergen.

Common mistakes for the novice patch tester

  • To assume all positive patch test reactions are relevant e.g. the most likely positive and non-relevant reaction is to nickel
  • Underestimate the role of irritant contact dermatitis: consider exposure to irritants as well as allergens
  • There is no diagnostic test available for irritant contact dermatitis: it is often a default diagnosis and is subjective
  • With regards to treatment, remember to emphasize skin protection and skin care measures as well as allergen avoidance
  • Ignoring the role of immediate hypersensitivity reactions causing contact urticaria or protein contact dermatitis – which require a blood test or prick testing

Videos to watch:

Talk 36 Determining relevance of reactions

Patch testing diagnostic flow chart

We use the following algorithm to assist in making a diagnosis of the patient’s skin condition, and to explain the diagnostic process to patients. The features of the algorithm include the fact that the positive reactions do not necessarily lead to the diagnosis – they may not in fact be relevant to the patient’s skin condition.

The algorithm also incorporates irritant contact dermatitis, which is always an important differential diagnosis of allergic contact dermatitis, and may co-exist with allergic contact dermatitis. It also includes immediate reactions, as many patients are confused about what is tested by prick testing and what is tested by patch testing.

Finally, there are multiple lines for the diagnosis: there may be multiple contributing factors to the patient’s condition. It is not uncommon for a nurse to be allergic to an ingredient of a hand cleanser used at work, have an atopic background with an element of irritant contact dermatitis and have latex allergy as well. All of these factors need to be addressed to effectively treat the dermatitis.

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In addition to explaining the patient’s diagnosis, it is important to discuss management. Management depends on the diagnosis but providing advice on skin care, glove use and reduction or elimination of relevant exposures is also crucial.

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Managing the risk using the hierarchy of control

The risk of occupational contact dermatitis can be reduced significantly by following Occupational Health and Safety (OH&S) Hierarchy of Control – where action is required at multiple levels

Priority 1: Elimination

  • Removal of the cause of the problem if possible
  • E.g. If a irritating substance is not needed, it can be removed therefore the hazard is eliminated

Priority 2: Substitution

  • Replace the substance or activity with one of less harm
  • E.g. Using a more gentle hand wash or hand cleanser

Priority 3: Engineering

  • Introduction of engineering controls to change the way a task is done
  • E.g. Dishwasher in a kitchen vs handwashing dishes

Priority 4: Administration

  • Introduction of policies and procedures for safe handling of substances
  • E.g. Skin care plan implementation

Priority 5: Personal Protective Equipment (PPE)

  • Considered the last resort in order to protect workers from hazards in their workplace
  • Can range from masks, gloves, gowns, aprons etc.

Allergen Avoidance

If there are positive relevant reactions it is important to provide information on the allergen and how best to avoid it. Education should consist of:

  • Written Information including allergen name (including any synonyms), typical uses/ where commonly found and how best to avoid the allergen. The team at the Skin Health Institute have developed information sheets for use in the patch testing clinic. These are available on the PatchCams website Additionally information sheets about individual allergens are also available on the allergEAZE website and Chemotechnique website
  • Advising patients to check all their products for the relevant allergen
  • Explaining the allergy cannot be treated with desensitation therapy and will likely be lifelong

Videos to watch:

Talk 38 Patient education and patch testing

Talk 40 +45 Allergen Avoidance

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