What determines the location of welts?

[f95toli]

I believe I have a general understanding why hives/welts occur as the result of a allergic reaction. However, I was wondering if it is know what determines the location of the individual welts?
When the reaction is due to the physical contact is is pretty obvious; but if it a reaction due to say food allergy less so.

I realize that it is to some extent probably random; but unless the "generation" of a welt somehow makes other welts less likely that still doesn't explain why you typically only get a few of them; and not hives all over your body.

Is there something special going on with the skin at the locations where welts are most likely to occur?

 

[jim mcnamara]

If I got what you mean - like a strawberry induced rash - these are called urticaria.

https://acaai.org/allergies/allergic-conditions/skin-allergy/

The location is a response of mast cells in surficial blood flow to an allergen
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6526977/

The location of an outbreak is somewhat random, but has a greater chance of repeating near the original outbreak. This causes a "cluster" effect sort of.

Location:

Mast cells are found throughout the body in loose connective tissue. Some are randomly dispersed in the tissue. They tend to concentrate near blood vessels, where the cell is more elongated. In the skin, concentrates can also be found near follicles, sebaceous glands, and sweat glands

--- https://www.ncbi.nlm.nih.gov/books/NBK499904/

 

[f95toli]

Yes, that is what I meant.

That is very interesting, I had no idea that was the mechanism!

Also, thanks for the great link!

 

[DaveC426913]

I suspect they're related to auto-immune disorders.

I have patches of eczema in particular places on my body - one knuckle, and now (frustratingly) the part of my nose which I am just now learning seems to be called the glabula or procerus.

So something in the flesh of those particular places is hyper-sensitive to stressors.

 

[jim mcnamara]

Um, how about what some researchers think:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7184931/

There is a considerable unmet demand for safe and efficacious medications in the realm of autoimmune and inflammatory diseases. The fate of the immune cells is precisely governed by control of various metabolic processes such as mitochondrial oxidative phosphorylation, glycolysis, fatty acid synthesis, beta-oxidation, amino acid metabolism, and several others including the pentose phosphate pathway, which is a unique source of metabolites for cell proliferation and maintenance of a reducing environment.

What this says is metabolic disease is a likely primary precursor to autoimmune disease. And the precursor to this, mitochondrial dysfunction, is a highly probable ultimate "starting point". Oxidative stress from unhandled ROS (reactive oxygen species) from glycolysis is the biochemical explanation. It generates inflammation which "trashes" mitochondria.

Metabolic Disease is, in a very big way, environmental. It is also called metabolic syndrome.
For some patients there can also be an additional genetic causes.
This link is for non-biologists:
https://www.nhlbi.nih.gov/health/metabolic-syndrome
A simple 'do I have metabolic disease test":

Do a waist circumference (C),
then do the hips (H).

If $C>H$ then the answer is really very likely to be 'yes'.

Please consider this a better explanation than just guessing.... it is an important concept in public health. BTW.