# \[MED Q\]: WHY does tar help psoriasis **URL:** \ **Category:** Factual Questions\ **Created:** [September 10, 2002, 10:06pm UTC](https://boards.straightdope.com/t/med-q-why-does-tar-help-psoriasis/127853 "2002-09-10T22:06:35Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Charlie\_Tan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/charlie_tan/32/12582_2.png) [@Charlie\_Tan](https://boards.straightdope.com/u/Charlie_Tan)\ **Post date:** [September 10, 2002, 10:06pm UTC](https://boards.straightdope.com/t/med-q-why-does-tar-help-psoriasis/127853/1 "2002-09-10T22:06:35Z")
To start with, yes I’ve googled. I’ve asked my dermatologist. No, I can’t find an answer. I have psoriasis for about 30 years. I’ve learned to live with it and I normally get by with sunshine, stereoids and stuff. But dad (he’s got it too) gave me a solution which contains tar. Though it won’t cure (there is no cure), it certainly helped. A lot. When googling I find lots of sites saying “Tar has been used for 100-150 years as a treatment to…” yada-yada. Well I know that. But smearing the body with tar seems a bit … snake-oilish to me. It does work, though. So why? The “it’s been around for a long time and it works” is not good enough for me. Surely some scientist must have tried to figure out why, by now. My dermatologists says: _mumble-mumble-mumble_ … because it does … _mumble-mumble_ ---
**Author:** ![miatachris](https://avatars.discourse-cdn.com/v4/letter/m/c0e974/32.png) [@miatachris](https://boards.straightdope.com/u/miatachris)\ **Post date:** [September 11, 2002, 12:37am UTC](https://boards.straightdope.com/t/med-q-why-does-tar-help-psoriasis/127853/2 "2002-09-11T00:37:38Z")
The truth that no one wants to hear is… we don’t know. There are many drugs out there that we do not know the mechanism of action on. Aspirin is the one that always leaps to mind when I explain this to people. When you tell people that you’re living in a world that doesn’t know how aspirin works, it usually gives them pause. If the coal tar is actually working for your psoriasis, count yourself lucky and try not to worry about the mechanism. There are millions out there who can’t get any relief at all and would not care whether or not the mechanism of action is known. I always find it the best policy not to lie to people, which is probably why your dermatologist is mumbling something like “nobody knows”. miatachris, R.Ph. ---
**Author:** ![Celyn](https://avatars.discourse-cdn.com/v4/letter/c/9dc877/32.png) [@Celyn](https://boards.straightdope.com/u/Celyn)\ **Post date:** [September 11, 2002, 12:59am UTC](https://boards.straightdope.com/t/med-q-why-does-tar-help-psoriasis/127853/3 "2002-09-11T00:59:35Z")
N.B.W - Nature Being Weird! But since I might as well have to have mine dealt with soon, and knowing it doesn NOT go away exactly, I reckon I will go along with anything suggested. The coal tar shapoo etc does rather smell though.☹ ---
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [September 11, 2002, 1:26am UTC](https://boards.straightdope.com/t/med-q-why-does-tar-help-psoriasis/127853/4 "2002-09-11T01:26:20Z")
> [@](#): > > \*Originally posted by miatachris \* > \*\*The truth that no one wants to hear is… we don’t know. > > There are many drugs out there that we do not know the mechanism of action on. Aspirin is the one that always leaps to mind when I explain this to people. When you tell people that you’re living in a world that doesn’t know how aspirin works, it usually gives them pause. > \*\* True perhaps 10 years ago, but we now do know how aspirin works, with the knowledge of prostaglandins and cyclooxygenates I and II. ---
**Author:** ![LolaBaby](https://avatars.discourse-cdn.com/v4/letter/l/d2c977/32.png) [@LolaBaby](https://boards.straightdope.com/u/LolaBaby)\ **Post date:** [September 11, 2002, 1:47am UTC](https://boards.straightdope.com/t/med-q-why-does-tar-help-psoriasis/127853/5 "2002-09-11T01:47:08Z")
:eek: I have been searching for over an hour (thanks for giving me something to do!) but to no avail. I’m thinking about breaking it down into the chemical properties of coal tar, but even that hasn’t helped, separately. I’m curious too, as I have used it previously. ---
**Author:** ![choosybeggar](https://avatars.discourse-cdn.com/v4/letter/c/8c91f0/32.png) [@choosybeggar](https://boards.straightdope.com/u/choosybeggar)\ **Post date:** [September 11, 2002, 5:51am UTC](https://boards.straightdope.com/t/med-q-why-does-tar-help-psoriasis/127853/6 "2002-09-11T05:51:56Z")
From **Thami, G. P. & Sarkar, R. Coal tar: past, present and future. Clinical & Experimental Dermatology Clin Exp Dermatol 2002 Mar;27(2):99-103.** > [@](#): > > The exact mechanism of action of CCT (crude coal tar) is not completely understood. It increases the mitotic labelling index of epidermal keratinocytes and also suppresses DNA synthesis which decreases the net mitotic rate of the epidermis. These effects are greatly enhanced by subsequent irradiation of the treated skin with UVA but not with UVB or UVC. > [@](#): > > Others argue that CCT inhibits enzymes, glucose-6 phosphate dehydrogenase and nicotinamide adenosine diphosphate enzymes, thereby suppressing the pentose cycle (which is particularly active in psoriasis). > [@](#): > > atrophogenic effect on the human epidermis. Lavker et al. demonstrated that following two weeks of CCT application, hyperkeratosis (build up of skin layers) and acanthosis (loosening of bonds between cells) result and are probably due to the irritant effects of CCT. Conversely, continued use for 6-8weeks leads to thinning of the epidermis and retention hyperkeratosis of the stratum corneum. \*\*The atrophogenic effect of CCT manifests clinically by the decreased thickness of plaques of psoriasis with prolonged application. \*\* CCT is a complex mixture and from my quick scan, little is known regarding the pharmacology of particular components. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [September 11, 2002, 1:08pm UTC](https://boards.straightdope.com/t/med-q-why-does-tar-help-psoriasis/127853/7 "2002-09-11T13:08:21Z")
I get by on sunshine. My forehead is a disaster unless I get doses of sunshine. Bizzare. And when I reach for the coal tar shampoo, I always wonder how it works. I always thought it put a thin coating on and helped the skin maintain moisture balance - I know that is wrong, but I had to picture it working somehow.