To understand what Nicotine Salts are you must first understand how traditional eliquids are made. Traditional eliquids are made with what's called "Freebase Nicotine". The basic recipe of these types of eliquids is: VG solution + PG solution + Flavoring + Freebase Nicotine. Some may say that is oversimplifying it. However, that is indeed the basic recipe.
Now, what is Freebase Nicotine? It's basically nicotine in its purest form. Basically a liquid form of nicotine. Similar to how isopropyl alcohol is in its basic form. There are many types of isopropyl alcohols. There is 50% isopropyl alcohol; there's 60% isopropyl, 70% and so on. However, the purest form of isopropyl alcohol comes in 91% or above. The higher the percentage, the more pure it is. This is the same with Freebase Nicotine. However, nicotine in this form tends to be very acidic and thus produces a harsh burn in the throat when vaped. This is where Nicotine Salts come into play.
Nicotine Salts Eliquid (or just "Nicotine Salts" for short) are a brand new form of eliquid that is very different from traditional "freebase" nicotine eliquid. Nicotine Salts contain a crystallized version of nicotine that comes dissolved in VG and PG solutions. Crystallized nicotine occurs naturally in tobacco plants and produce a much smoother hit than traditional freebase nicotine eliquids. If you've ever vaped traditional eliquid, you might notice a burning sensation in your throat. Some of you might find it difficult to vape 6mg, 12mg or even 18mg nicotine eliquid. This is because of the acidity the Freebase Nicotine has. However, Nicotine Salts do not produce this burn. Again, nicotine salts produce a much smoother, more soothing vaping experience and is not harsh on your throat.
In addition to this, if you combine the smoothness of nicotine salts with a low wattage device such as the iCare by Eleaf, the Suorin Air, or the Limitless Pulse Mod, you will receive a much smoother vape hit that is not only easier on your throat but will give you a faster, more satisfying nicotine sensation as well. However, since Nicotine Salts are much higher in nicotine strength, they can result in what's called a "Nicotine Headache". Experts recommend waiting around 6 seconds between each hit when vaping nicotine salts. This will allow your body's cells enough time to recuperate and prevent a headache from happening.
So there you go! Now you have an understanding of what Nicotine Salts are and why they are the newest innovation in the vaping world.
NOTE: It is possible to vape nicotine salts with high wattage devices such as the Smok Alien 220W Kit or the Vaporesso Revenger. However, it is not recommended.