Americans have been using topical arthritis medicines for more than a century. Sloan’s Liniment, for example, was originally developed in the 19th century by harness maker and self-taught veterinarian Andrew Sloan. It was intended for use on horses to ease their muscle pain.

Andrew’s son Earl later developed a thriving business selling Sloan’s liniment to people with arthritis, back pain, sore knees, rheumatism, lumbago, strains and sprains. He advertised it as “good for man and beast.”

The main ingredient in Sloan’s Liniment was capsaicin (the essence of hot chili peppers). It also contained menthol, methyl salicylate, camphor and oil of turpentine. It became extremely popular and profitable.

Many other old-fashioned topical arthritis remedies made use of one or more of those ingredients, too. They included Bengay, Mentholatum ointment, Tiger Balm and Vicks VapoRub.

Fast forward to the 21st century. Advil (ibuprofen) is an extremely popular over-the-counter oral pain reliever. This nonsteroidal anti-inflammatory drug (NSAID) became available without a prescription in 1984. Prior to that, ibuprofen was available only by prescription. Doctors often prescribed it under the brand name Motrin. OTC Motrin IB came out later.

Early last year, the maker of Advil took advantage of its brand name recognition. The company brought out a topical pain reliever called Advil Targeted Relief. This pain-relieving cream looks ultra-modern and high-tech. It comes with a fancy applicator cap.

The ingredients, however, would have sounded quite familiar to the liniment makers of the 19th and 20th centuries: camphor, capsaicin, menthol and methyl salicylate. What was old is new again.

Scientists believe that capsaicin works by depleting substance P from the nerves of the skin. It may also affect transient receptor potential (TRP) channels on those nerves. Both TRPA1 and TRPV1, which respond to capsaicin, contribute to joint pain in arthritis and gout (Pharmaceuticals, Oct. 15, 2018).

You may not be surprised to learn that methyl salicylate also affects TRPV1 (Molecular Pharmacology, February 2009). Both menthol and camphor, on the other hand, activate TRPM8, which affords a cooling sensation on the skin along with pain relief (Chemical Senses, September 2013).

A reader with knee arthritis shared that she uses a topical pain reliever containing camphor, capsaicin, menthol and methyl salicylate. She reported that this combination is “very effective. I have found that I do not need to take Advil or any other oral pain drugs.”

Some readers may find the latest topical arthritis treatments confusing, however. Voltaren Arthritis Pain Gel, which has been available for nearly two decades, contains a nonsteroidal anti-inflammatory drug called diclofenac. This NSAID is also found in oral prescription pain relievers but not in OTC pills.

Aleve is a very popular OTC oral NSAID. The active ingredient is naproxen. The manufacturer appears poised to introduce its own topical gel under the name Aleve Arthritis Pain Gel. Instead of naproxen, it contains diclofenac.

It would be easy for people to get all these different pain products mixed up. Just as the ingredients differ, so do the mechanisms of action. Precautions and side effects vary substantially from one product to the next, too.

Just because the brand is familiar, don’t assume you know what is in the tube. Read the label and ask your pharmacist if the pain reliever you are purchasing is appropriate for your condition.

In their column, Joe and Teresa Graedon answer letters from readers. Write to them in care of King Features, 300 W. 57th Street, 41st Floor, New York, NY 10019, or email them via their website: www.PeoplesPharmacy.com.