This document summarizes different types of contact dermatitis, their causes, pathogenesis, and complications. There are three main types - irritant, allergic, and photocontact dermatitis. Irritant contact dermatitis results from single exposure to strong irritants like solvents and soaps. Allergic contact dermatitis occurs from repeated exposure to mild irritants like metals and causes an immune response. Photocontact dermatitis involves skin exposure to certain rays along with an allergen or irritant. Complications can include infection if the skin is broken, thickening of the skin, or a bacterial infection of the skin called cellulitis.

2. TYPES OF CONTACT
DERMATITIS
1. IRRITANT CONTACT DERMATITIS:
 Most common and non- allergic type of
contact dermatitis.
 Occurs mostly due to strong irritants
after single exposure.
2. ALLERGIC CONTANT DERMATITIS:
 Triggers immune response.
 Occurs mostly due to mild irritants after
repeated exposures.
3. PHOTOCONTACT DERMATITIS:
 occurs when the allergen or irritant is

3. CAUSES
1. IRRITANT CONTACT DERMATITIS:
 Solvents like alcohol, acetone, ketone & esters.
 latex, kerosene & ethylene oxides
 surfactants in topical medications and cosmetics
 Soaps, detergents and cleaning products.
2. ALLERGIC CONTACT DERMATITIS
 Metals like nickel, chromium, gold etc.
 Ragweed pollen, spray &insecticides
 Drugs like penicillin
 Dyes
3. PHOTOCONTACT DERMATITIS:
 Various rays such as UV rays.

4. 1. ALLERGIC TYPE:
 Memory T-cell mediated delayed type
PATHOGENESIS:
Haptens + Keratin protein
Sensitization by APCs like Langerhans cells &
dendritic cells
Haptens migrate to lymph node and initiate
adoptive immune response
Amplification of memory T-cells and helper T-cells
Activation of CD8+ cells, gamma interferons, interleukins,
cytokines etc by helper T-cells on reexposure leading to skin
inflammation, itching, and the typical rash of contact dermatitis.

5. 2. IRRITANT TYPE
 Antibody mediated hypersensitivity
 Physical and chemical irritants that contact
the skin, damage epidermal cells and remove
epidermal lipids from the epidermis.
 An increase in skin permeability and trans-
epidermal water loss occurs.
Activation of innate immune system
Induce expression of cytokines and chemokines
Causes inflammation

6. Irritant type
1.Activation phase
 Bacteria is phagocytosized by APCs
 Combine with MHC-II proteins and present on surface of APC
 Recognised byTcell cd4+ and bind to MHC-II complex
 Release cytokinins IL-2 which activates helper Tcell
 Activated helper T cell release IL-2 causing T cell proliferation
2.Effector phase
 IGM binds to effector complex
 Engulfed by B cell and phagolysosome is formed
 Binds to MHC II protein And present on surface of B cell
 Helper T cell binds to complex and release cytokinins
 Cytokinin stimulate B cell and proliferate B cell
 B cell differentiate into [plasma cell and memory cell
 Release antibodies in lock key fashion
 Phagocytosis and lysis of bacteria
 Complement is activated and it attacks and puncture hole in
bacteria.

7. 3.Photocontact type
Alteration of gene by various rays
Coding of altered protein
Altered protein acts as antigen

8.  Infection
Skin that is moist from oozing or open
from irritation or scratching is
susceptible to infection from bacteria
and fungi. The most common types of
infection are staphylococcus and
streptococcus. These can lead to a
condition called impetigo.
COMPLICATION

9.  Neurodermatitis
skin may become thick, discolored, and
leathery.
 Cellulitis
Cellulitis is a bacterial infection of the
skin. It’s most often caused by
streptococcus or staphylococcus bacteria.
The symptoms of cellulitis include fever,
redness, pain, chills, and aches in the
affected area.

10. SOURCES
1. Anantanarayan and Paniker’s Textbook Of
Microbiology
2. Robbins And Cotran Pathologic Basis of Disease
3. Online Sources