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irritant and contact sensitizer treatments for alopecia areata overview

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Contact dermatitis inducers: Dinitrochlorobenzene (DNCB), diphenylcyclopropenone (DPCP), squaric acid dibutyl ester (SADBE) - how they are believed to work

The difference between an irritant and a contact dermatitis inducer is a bit vague. Clinically, the effects of an irritant are much the same as a contact sensitizing chemical with inflammatory dermatitis induction being the key symptom. Essentially, an irritant treatment for alopecia areata acts by disrupting the normal cell growth and differentiation in the skin. This physical damage then stimulates the immune system to respond to clear up the problem and limit the skin damage. A contact dermatitis inducer is a chemical that the immune system is responsive (allergic) to. It may not have a direct action on the skin cells. Rather, the skin immune system identifies the molecules of the chemical as something it should respond to. The resulting inflammation will cause skin dermatitis that varies in severity with each individual depending on how allergic the person is to the contact dermatitis inducing chemical.

The popular belief is that irritants and contact dermatitis inducers work as antigenic competition. That is, the irritant chemical applied to the scalp is far more interesting to the inflammatory cells than the hair follicles. Thus the cells move away from the hair follicles and towards the skin surface where the irritation induced skin damage is or where the contact sensitizer chemical is present. It would seem the cells find the skin damage or irritating chemical much more of a threat than any hair follicle antigens.

However, this assumes that the cells responding to the irritant or contact dermatitis inducer are the same as the cells responding to the hair follicle antigens. I don't agree with this idea. I think the chemical irritation/contact sensitization induces inflammation from a mostly new group of cells and in doing so causes a change in the cyotkine environment of the skin. Cytokines are hormone like chemicals that are produced by inflammatory cells to communicate with each other. Some cytokines excite immune cells to attack and destroy, other cytokines tell immune cells to calm down and go home. I think there might be a change in the cytokine response that encourages cells to move away from the hair follicles and into the upper skin layers and/or to leave the skin entirely. There is some research to suggest irritants cause cytokine production levels to change.


Contact dermatitis inducers: Dinitrochlorobenzene (DNCB), Diphenylcyclopropenone (DPCP), Squaric acid dibutyl ester (SADBE) - how treatment is given.

DNCB (Dinitrochlorobenzidine), DPCP (Diphenylcyclopropenone or Diphencyprone), and SADBE (Squaric acid dibutyl ester) are topical contact sensitizers. They are primarily used for people with extensive scalp hair loss as opposed to patchy hair loss. Given these treatments are mostly used by people with long term extensive hair loss each has a relatively good success rate in growing cosmetically acceptable hair when treatment is given by a dermatologist experienced in their use. Less experienced dermatologists may have a lower success rate and possibly a higher incidence of side effects. The allergic response the body makes to the chemical(s) results in good hair regrowth with claims of a 38% success rate for DPCP (Shapiro 1993), 63% for DNCB (Swanson 1981) and up to 70% for SADBE (Flowers 1982). However different investigators report different success rates for the same contact sensitizer. For example, in using SADBE some investigators report only a 50% chance of response (Case 1984, Johansson 1986), or even less (Valsecchi 1986, Caserio 1987). The variability in success rates varies at least in part due to different investigators' different definitions of what constitutes successful regrowth (ie success = light fuzz?, patchy regrowth?, total recovery? etc).

DNCB is not very popular as it has been shown to be potentially mutagenic at high doses (Krakta 1979). However, there are no reports of people treated with low dose DNCB for alopecia areata ever having any side effects of this nature. DPCP and SADBE are known not to be mutagenic (Strobel 1980), but their is a lack of specific information on toxicity to be sure of their true safety. DPCP and SADBE seem to be replacing DNCB use outside of the USA (DPCP has not been passed for official use in the US and so is not widely available there). DPCP and other contact sensitizers do have side effects. As a sensitizer a chemical should have a desired effect of causing scalp itching and redness. This irritation is important as this is necessary for the treatment to work. For some people this inflammation can become excessive and cause undesired blistering, skin peeling, and even some skin scarring. Other patients have reported swollen lymph nodes, hives, and decreased/increased pigment production in the area of application.

When sensitizing agents are used to treat alopecia areata, the dermatologist should first apply a small dose of the chemical at quite a high concentration to a patch of skin and monitor the reaction. This initial application is to "sensitize" the immune system to the compound. If you have a skin reaction then you should be suitable for treatment.

The dermatologist should then apply a larger dose of a very dilute solution of the chemical. If you have a reaction then that is the concentration you will use for long term treatment. If there is no reaction then stronger and stronger chemical concentrations will be applied until a skin reaction is obtained. It is important to define a minimum dose that works for each person as some people are much more sensitive to the chemicals than others. One chemical concentration may be good for some people but too strong for others. Excess irritation in sensitive people may cause excessive skin blistering and other side effects. Finding the correct dose for you may take several visits to the dermatologist over several weeks.

This individual had complete scalp alopecia. They have been treated only on one half of the scalp with DPCP. The other half was not treated. This is one method used by some dermatologists to make usre that the sensitizing agent can actually promote hair growth. Once hair growth is apparent on the treated half of the scalp, the other half is treated too.

Once the correct dose has been found the frequency of treatment is determined. Application may be required once a week in the initial stages to kick start hair growth. Later the frequency of application may be reduced to a maintenance dose. As with all forms of alopecia areata treatment the chemicals have to continue to be applied and continue to induce a skin reaction for hair growth to persist. If you stop the treatment the hair will gradually fall out again.

When an irritant treatment is correctly applied you should develop a red rash and feel itchy but nothing more. The dermatologist will recommend you keep the irritant on your scalp for a period of time that varies depending on how sensitive your skin is and the personal preference of the dermatologist. You may have to avoid washing your scalp for several hours or even a couple of days depending on your dermatologists recommendations. You may also be directed to cover your scalp when outside as sunlight degrades such chemicals as DPCP and SADBE rendering them ineffective. Because DPCP and SADBE are biodegradable they have a limited storage life and solutions have to be made up fresh on a regular basis.

Because of the irritation from the chemicals it is important not to touch your scalp or let any one else touch it with their bare hands. You do not want to spread the irritant to other areas of skin or to other people. You may have to cover your head, especially when sleeping, to stop the irritant spreading and getting onto bedclothes and eventually on to your face or worse, your partner.

If the treatment works and hair growth develops some dermatologists will trust you to apply the irritant chemicals yourself as a maintenance dose at home. Other dermatologists believe the chemicals are too powerful, could be inappropriately applied by the patient, and will want you to attend the dermatology clinic to ensure safe and proper treatment.


Treatment of alopecia areata with irritants and sensitizers references

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