I've given away hundreds of pounds over the years, to grateful recipients. It comes in 50 lb bags, as ice-melting salt for porches, etc. Look under "salt" in local phone books for suppliers. Costs about $23 / 50 lbs in Ohio, including tax. Also sold in 2, 5 and 10 pound containers for marine aquarium use, and for human use (see Ebay for best prices).
It's first use is for nerves and sleep. In a non-survival situation, a cup of the crystals added to a hot tub of bathwater, relaxes sore muscles and joints as well as strongly aiding in sleep. If I remember correctly, magnesium ions activate benzodiazepine (Valium) receptors. In a survival situation, a spray bottle is used to apply it. Spray it on, and run your fingers over it lightly to maximize contact with skin. It efficiently absorbs through the skin and effects the same results. It is also an anti-inflammatory, and I have given spray bottles to three individuals who used it on swollen arthritic knees. One could watch them return to normal size in about 15 minutes.
One variety is MAG brand, which I have bought repeatedly. It is eminently non-toxic. Also a potent anti-bacterial. I've used it for a couple of soft tissue infections, and for the pain of toothaches, until I could see a dentist. Overuse can cause hypermagnesemia (too much magnesium in the blood). I induced this in myself purposefully, and recovered quickly. Mostly a sleepy, befuddled state that lasts a while. Overuse can also cause fungal overgrowth in the body, so don't drown yourself in it. Doesn't need to be refrigerated. Also, it is a salt, so don't spray in eyes, nose, on cuts or burns, and the like. Won't stain cloth.
Have also used this for many years. Have given much away, and again, the recipients were grateful. Acts as a long-lasting local anesthetic, especially in cases of osteoarthritis. And as an antibacterial, topical or transdermal. Like magnesium chloride, I've used it for toothaches and a couple soft tissue infections. Must be diluted to between 70 and 80 percent DMSO with distilled or otherwise purified water. DMSO generates heat upon mixing with water, and applying the usual 90 or 99 percent without dilution can actually cause skin burns. Diluted, though, it's fine. At less than 70% strength, it loses a significant part of it's antibacterial ability.
DO NOT allow it to become contaminated with anything, as it will carry almost anything right through the skin and into your internal tissue and bloodstream (don't try to use this quality for getting drugs into the body, as it it is unpredictable). Like magnesium chloride, does not need to be refrigerated. Mainstream medicine cries over one small animal study that produced cataracts. However, any parallels in humans are dubious, and I have used it on my face, on occasion, over long periods of time without any change to my vision. Ebay is a good source for 99.9% DMSO in 16 ounce (non-endocrine disruptor) plastic bottles, on the cheap. The negative is that it can give one garlic breath for some days. Won't stain cloth.
A focus in my medical research in the past year. Listed in the Merck Index of Chemicals and Biologicals (a reference work about chemicals) as a "cellular proliferant". It also is a keratolytic (eats scar tissue). Whereas healing equals the formation of scar tissue, regeneration (what allantoin does) is making a site of injury as it was before. All mammals except apes and humans have a gland in the umbilical cord (the Allantois gland) which produces allantoin, which makes the fetus grow much more rapidly).
The Comfrey plant produces allantoin, as well as several B vitamins. Folic Acid (a B vitamin, scroll down to next entry) is necessary to have the finest effects with allantoin. The problem with natural allantoin from this source is that the Comfrey plant also produces toxic pyrrolidizine alkaloids which poison the liver, even if taken in small amounts repeatedly. Nonetheless, a tea made from Comfrey leaves is colloquially known as "Knitbone", as it very much speeds up the healing of broken bones. Consider that bones have a very poor blood supply, which emphasizes the power of this alkaloid. Mainstream medicine is hysterical in warning people against using allantoin - Comfrey - Healer or Poison?
However, doctors and scientists, working for the medical industrial complex, fail to mention that there is synthetic allantoin that can not have these alkaloids as a contaminant. I buy it by the pound. I won't mention from who, only that it took some time to find a supplier that doesn't have crazy charges for postage. If you buy some, email the company first, and make sure theirs is synthetic.
Besides healing tissue rapidly and well, allantoin also improves memory, is antidiabetic, is antihypertensive , has been used to heal gastric and duodenal ulcers, to which I can personally attest, and has been used to heal ulcers of the leg (it is partly responsible for the healing qualities noted when maggots are used to debride, or remove dead and infected tissue in hospitals). It is also very non-toxic. I took 5 grams orally and daily for about a month, and have adjusted my dose to 2.25 grams / day. I note no negative effects.
I've also treated wounds with allantoin, and they healed as if new. A friend of mine wrecked her bicycle and went over the handlebars, face first, onto the sidewalk. She wasn't injured too badly, short of some "road burn". It did look bad, though. I dissolved allantoin in distilled water, decanted it from the undissolved portion, and put it in a spray bottle. I told her to keep it refrigerated (the solution will spoil if kept at room temp). I told her to wait until 15 minutes before she went to sleep, spray her face, smooth it out with her fingers to maximize contact with her skin, and avoid contact with cloth for 15 minutes. She also took a high dose of Folic Acid daily. Within two weeks, not only was her face healed (except for a small internal "knot" under her lip), but people told her she looked younger. One can imagine the usefulness of this in a survival situation, as well as in everyday life. And it's cheap.
It's a nutrient, so it;s necessary to maintain life and health. I and my local friends take 1000 ucg / day. Ebay, once again, allows for the best price. I buy bottles of 240 capsules, which seems the most economical. I can't imagine why anyone wouldn't take this daily, as no new cell growth (healing or regeneration) is possible without it. Docs only recommend it for pregnant women, but I think everyone should take it. I take it specifically for the synergistic effect with allantoin. Some people say they lack an enzyme, and must take a different form of Folic Acid.
I am not a doctor, thank goodness, and I am not giving anyone medical advice. Blah blah blah...