Magnesium is usually excreted by the kidneys. When taken orally it will remain in the bowel causing a loosening effect.

It is very odd that you are getting loosening from a topical product. The transdermal nature of the base may be carrying something else thru your skin.
Ingredients list here:
http://kirkmanlabs.com/ProductKirkma...mSulfateCream/
I don't know about all these ingredients in detail.

Or I wonder if you are using too much? If you only apply to one ankle and the next day to the other, that might work.

Or switch to the Morton brand. I have no problems with Morton's.
And I am very sensitive to GI loosening with all the oral products including the SlowMag. That Kirkman product was initially designed for children, and hence to be used in smaller amounts per application.

Morton Epsom lotion is only $5.95 at WalMart and online at Amazon. One 8 oz bottle lasts me 3months or longer.

If you have hereditary angioedema causing your swelling, you could have the GI form (like I do) and if so I'd get that checked out. Blood work for Complement #4 and C-1 inhibitor levels.
http://en.wikipedia.org/wiki/C1-inhibitor.

It might be a good idea to email Kirkman with your question too, about their product and possible GI effects.