Acute ICD is caused by contact to a potent irritant. Substances that cause necrosis are called corrosive and include acids and alkaline solutions. Contact is often accidental at the workplace. Cosmetics are unlikely to cause this type of ICD because they do not contain primary irritants in sufficient concentrations.
Symptoms and clinical signs of acute ICD develop with a short delay of minutes to hours after exposure, depending on the type of irritant, concentration, and intensity of contact. Characteristically the reaction quickly reaches its peak and then starts to heal; this is called ''decrescendo phenomenon.'' Symptoms include burning rather than itching,
stinging, and soreness of the skin, and are accompanied by clinical signs such as erythema, edema, bullae, and even necrosis. Lesions are usually restricted to the area that came into contact, and sharply demarcated borders are an important sign of acute ICD. Nevertheless, clinical appearance of acute ICD can be highly variable and sometimes may even be indistinguishable from the allergic type. In particular, combination of irritant and allergic contact dermatitis can be troublesome. Prognosis of acute ICD is good if irritant contact is avoided.
For some chemicals, such as anthralin, it is typical to produce a delayed acute ICD. Visible inflammation is not seen until 8 to 24 hours or more after exposure . Clinical picture and symptoms are similar to acute ICD. Other substances that cause delayed acute ICD include dithranol, tretinoin, and benzalkonium chloride. Irritation to tretinoin can develop after a few days and results in a mild to fiery redness followed by desquamation, or large flakes of stratum corneum accompanied by burning rather than itching. Irritant patch-test reactions to benzalkonium chloride may be papular and increase with time, thus resembling allergic patch-test reactions . Tetraethylene glycol diacrylate caused delayed skin irritation after 12 to 36 hours in several workers in a plant manufacturing acrylated chemicals .
Irritants may produce cutaneous reactions that do not meet the clinical definition of a ''dermatitis.'' Irritant reaction is therefore a subclinical form of irritant dermatitis and is characterized by a monomorphic rather than polymorphic picture. This may include one or more of the following clinical signs: dryness, scaling, redness, vesicles, pustules, and erosions . Irritant reactions often occur after intense water contact and in individuals exposed to wet work, such as hairdressers or metal workers, particularly during their first months of training. It often starts under rings worn on the finger or in the interdigital area, and may spread over the dorsum of the fingers and to the hands and forearms. Frequently, the condition heals spontaneously, resulting in hardening of the skin, but it can progress to cumulative ICD in some cases.
Cumulative ICD is the most common type of ICD . In contrast to acute ICD that can be caused by single contact to a potent irritant, cumulative ICD is the result of multiple subthreshold damage to the skin when time is too short for restoration of skin-barrier function . Clinical symptoms develop after the damage has exceeded a certain manifestation threshold, which is individually determined and can vary within one individual at different times. Typically, cumulative ICD is linked to exposure of several weak irritants and water contact rather than to repeated exposure to a single potent irritant. Because the link between exposure and disease is often not obvious to the patient, diagnosis may be considerably delayed, and it is important to rule out an allergic cause. Symptoms include itching and pain caused by cracking of the hyperkeratotic skin. The clinical picture is dominated by dryness, erythema, lichenification, hyperkeratosis, and chapping. Xerotic dermatitis is the most frequent type of cumulative toxic dermatitis . Vesicles are less
frequent in comparison to allergic and atopic types ; however, diagnosis is often complicated by the combination of irritation and atopy, irritation and allergy, or even all three. Lesions are less sharply demarcated in contrast to acute ICD.
Prognosis of chronic cumulative ICD is rather doubtful [63,64]. Some investigators suggest that the repair capacity of the skin may enter a self-perpetuating cycle .
This term is often used similarly to cumulative ICD [55,60]. Clinically, the two types are very similar as well. According to Malten and den Arend, traumiterative ICD is a result of too-early repetition of just one type of load, whereas cumulative ICD results from too-early repetition of different types of exposures .
Exsiccation eczematid is a subtype of ICD that mainly develops on the extremities. It is often attributable to frequent bathing and showering as well as extensive use of soaps and cleansing products. It often affects elderly people with low sebum levels of the stratum corneum. Low humidity during the winter months and failure to remoisturize the skin contribute to the condition. The clinical picture is typical, with dryness, ichthyosiform scaling, and Assuring. Patients often suffer from intense itching.
Traumatic ICD may develop after acute skin traumas such as burns, lacerations, and acute ICD. The skin does not heal as expected, but ICD with erythema, vesicles and/or papu-lovesicles, and scaling appears. The clinical course resembles that of nummular dermatitis .
Pustular and acneiform ICD may result from contact to irritants such as mineral oils, tars, greases, some metals, croton oil, and naphthalenes. Pustules are sterile and transient. The syndrome must be considered in conditions in which acneiform lesions develop outside typical acne age. Patients with seborrhoea, macroporous skin, and prior acne vulgaris are predisposed along with atopics.
Nonerythematous ICD is an early stage of skin irritation that lacks visible inflammation but is characterized by changes in the function of the stratum corneum that can be measured by noninvasive bioengineering techniques [55,65].
Sensory irritation is characterized by subjective symptoms without morphological changes. Predisposed individuals complain of stinging, burning, tightness, itching, or even painful sensations that occur immediately or after contact. Those individuals with hyperirritable skin often report adverse reactions to cosmetic products with most reactions occurring on the face. Fisher defined the term ''status cosmeticus,'' which describes a condition in patients who try a lot of cosmetics and complain of being unable to tolerate any
of them . Lactic acid serves as a model irritant for diagnosis of so called ''stingers'' when it is applied in a 5% aqueous solution on the nasolabial fold after induction of sweating in a sauna . Other chemicals that cause immediate-type stinging after seconds or minutes include chloroform and methanol (1 : 1) and 95% ethanol. A number of substances that have been systematically studied by Frosch and Kligman may also cause delayed-type stinging [67,68]. Several investigators tried to determine parameters that characterize those individuals with sensitive skin, a term that still lacks a unique definition [69,70]. It could be shown that individuals who were identified as having sensitive skin by their own assessment have altered baseline biophysical parameters, showing decreased capacitance values, increased transepidermal water loss, and higher pH values accompanied by lower sebum levels . Possible explanations for hyperirritability (other than diminished barrier function) that have been discussed are heightened neurosensory input attributable to altered nerve endings, more neurotransmitter release, unique central information processing or slower neurotransmitter removal, and enhanced immune responsiveness [69,71]. It is not clear whether having sensitive skin is an acquired or inherited condition; most probably it can be both. As in other forms of ICD, seasonal variability in stinging with a tendency to more intense responses during winter has been observed . Detailed recommendations for formulation of skincare products for sensitive skin have been given by Draelos .
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