Dermatitis and Skin Disorders. Skin allergy patch testing.

With the ongoing cold and dry weather, skin disorders are coming up. With uncontrolled use of cosmetics, allergies to cosmetic products are on the rise too.

Patch testing is done for cosmetic products such as  PPD and  metals like nickel, chromium and various other chemicals.


Contact Dermatitis: Contact dermatitis is when an outside allergen comes in contact with your skin and causes allergic and/or irritant response. Irritation to external chemicals is more common.

Sometimes the skin can become red and angry due to hypereactivity

A systemic response like extreme redness of skin, especially on the buttocks can be seen.

Contact Urticaria: When you get a typical wheal and flare reaction to an external allergen. In extreme cases you can get an anaphylactic shock.

Irritant Contact Dermatitis

The skin will look glazed, parched or scalded, with a sharply circumscribed margin. Once you remove the external irritating agent, healing will start.

Atopic dermatitis:

  • There is a family history of atopy or allergic diseases
  • It’s common in early childhood due to food allergies. The child may grow out of most of them or develop allergic rhinitis,asthma or allergic conjunctivitis later on.
  • It is characterized by dry, scaly and itchy lesions, in early childhood and babies this is a rash on the face, back of joints
  • In adolescents and young adults it is more common in the folds of the elbow and knee joints, armpit, groin, etc.
  • It can be treated by avoiding the allergen, allergy skin prick tests to identify the cause. Local emollient creams help.
  • Immunotherapy will help control the disease, prevent development of other allergies and prevent progress to further complications.

Seborrheic Dermatitis: It is common in areas like the scalp, face and chest. It is related to sebum or the greasy substance produced by the sebaceous glands in the skin.

  • It is common in cold weather, and can be triggered by stress
  • It is seen in infants, healthy young people, but can be common in people with Parkinson’s or HIV infection.
  • It is not related to diet.
  • It is caused because of a yeast like fungus in the skin.


  • Reddish areas covered with greasy looking white or reddish skin scales.
  • In the scalp: It could result in mild flakes leading to dandruff, or a redder, scalier weeping rash. Cradle cap in infants could be due to seborrheic dermatitis
  • On the face: It affects the inner part of the eyebrows, the crease on the side of the nose, and the cheeks. Eyelids can become red, sensitive and inflamed.(blepharitiS)
  • Ears:  the skin behind the ear can show reddish scaly lesions. the ear canal and Pinna too. It can lead to Otitis externa.
  • Chest : Front of the chest.
  • Folds: Elbow, armpit, knee, groin. In children the nappy area is affected.

Treatment: Treatment with seborrheic dermatitis has to be continued. Once you stop the treatment the lesions tend to recur

On the scalp: 

  • Remove dense scales with olive oil.
  • Shampoos containing Zinc, selenium sulphide, or ketoconazole can be used. They should be kept for 10-15 minutes before rinsing them off.
  • Sometimes a strong steroidal cream will help.

Over the body: Mild steroidal and antifungal creams will help.

Ear canal: Antifungal creams used in the ear canal and antifungal/steroidal ear drops.

  • Application of olive oil can prevent, itching dryness and scaly lesions.

Regular use of a moisturizer or anti-fungal cream, shampoo, body lotion will help in control.

PSORIASIS: Dry silvery white scales like mica. On removal they leave a white patch with punctate bleeding.

Causes of Contact Dermatitis: 

  • Detergents are a very common cause of irritant contact dermatitis due to their strong caustic nature and they easily erode the skin barrier.
  • Cosmetics, eye shadows cause allergy too.
  • Transfer of nail polish to the eye and face
  • Benzalkonium chloride, a preservative in medicated eye and ear drops is one of the common causes. Thimerosal and neomycin sulphate are other ones.
  • Chemicals such as lanolin, coconut oil, etc
  • PPD, Balsam of Peru, Parabens, colophony and many others
  • Nickel, chromium and cobalt in costume jewellery
  • The above can also be responsible for rejection in orthopedic joint replacement surgeries.Once you have allergy in the skin to these chemicals, a systemic reaction can occur.
  • Ultraviolet light as exposure to sun Rays can worsen the reaction.

Occupational contact dermatitis is common in the following groups:

  • Food handlers like cooks and caterers
  • Health care workers
  • Persons involved in cleaning
  • Cosmetology
  • Painting
  • Heavy mechanics and assembling of parts
  • electronics
  • Construction
  • Agriculture, Forestry and Fishing
  • Printing and Lithography


In patch testing, chemical allergens and drugs are applied directly on the skin. They are left for 3 to 7 days. If there is an irritating lesion, from a mild rash to a severe reaction and vesicles, the patch test is said to be positive.

  • Readymade patches are available which can be applied to the skin.
  • The patches can be customised by using paste and applying pre cut linen patches covered by micropore or hypoallergenic dressing tape.
Allergy test being carried out on a woman's back.
Allergy test being carried out on a woman’s back.

Instructions for patch testing:

  • The patient should not be on oral antihistaminic, anti allergic or steroidal medication for at least 3 days before the patch test.
  • Topical application of corticosteroids and lotions to the skin should be avoided for 3 days prior
  • The patches are applied to the back or upper arm. During the period of the patch test the patient cannot take a bath or apply water to the patches.
  • The patient should not sweat otherwise the patches will come off. The patch test is typically done in cold weather, as summers can cause sweating.

Treatment of Contact Dermatitis

  • Avoidance of the chemical e.g. using long handled cleaning tools like wet mops and vacuum cleaners.
  • Substitution wherever possible with a less allergenic chemical
  • Job rotation so that periods of exposure are less
  • Protective gloves, face shields, aprons, uniforms, eye wear, etc
  • Emollient creams

Please contact your doctor for expert diagnosis and advice

Published by allergy care

I am an ENT specialist practicing allergy for the last 5 years. feel free to contact me

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