The use of topical pain cream is nothing new, in fact, many cultures have used topical cream to relieve pain for centuries. What is different in recent years? The difference is our level of understanding regarding how topicals work and how we can better tailor them to be more effective for certain types of soreness and discomfort. To better appreciate how topicals work in our system, we must have a basic understanding of how pain works. There are two types of pain; chronic and acute and both have various triggers that cause our body to react with a pain response.
The International Association for the Study of Pain has offered the following definition of acute pain: “Acute pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Thus, pain has sensory and affective components, as well as a cognitive component reflected in the anticipation of future harm.” To put these processes in simpler terms, the body receives external or internal stimulus that alerts the nervous system of tissue or possible tissue damage or injury. The signal travels through the nervous system to the brain where a response or reaction is processed and executed. Acute pain involves nerve endings and receptors in body tissues; that convey signals to the brain about the state of the body. Acute pain is provoked by a specific disease or injury, serves a useful biologic purpose, is associated with skeletal muscle spasm and sympathetic nervous system activation, and is self-limited. Simply put, the brain receives a message that something is wrong thus causing the feeling of soreness in the body. It also means that this type of discomfort is easier to understand as it presents in a more logical manner. For example, you play your first game of the season and you have a sore shoulder when you wake up the next day, basically a cause and effect type of pain that can be identified, isolated, treated and resolved.
“Chronic pain, in contrast, may be considered a disease state. It is pain that outlasts the normal time of healing, if associated with a disease or injury. Chronic pain may arise from psychological states, serves no biologic purpose, and has no recognizable end-point. Both acute and chronic pain are an enormous problem in the United States, costing 650 million lost workdays and $65 billion a year. The therapy of acute pain is aimed at treating the underlying cause and interrupting the nociceptive signals. The therapy of chronic pain must rely on a multidisciplinary approach and should involve more than one therapeutic modality.”
In both the definitions and explanations, pain is a function of nerves and receptors transmitting signals of warning to the brain, even in the case of chronic pain, the sensation manifests with physical symptoms like inflammation and stimulation of the same nerves and receptors whether they are triggered by physical or psychological stimulus. This is positive, as it gives us the ability to treat both acute and chronic pain in much the same way with respect to topicals. Now that we understand how pain signals and neurotransmitters move pain signals between body tissues and the brain, we can move on to the use of topicals for pain relief and how the many different preparations work to elevate symptoms.
As mentioned, Topical medications have been used to relieve pain symptoms for a very long time. Merriam-Webster defines Topicals, with respect to medication, as…
2: designed for or involving local application and action (as on the body)
a topical anesthetic
a topical remedy
Essentially, any medication that is prepared for direct application to the skin, either at the site of an injury or a placement known for its excellent sub-dermal absorption properties, is classified as a topical medication. With respect to topicals for pain relief the preparation is designed to be applied directly to the site of the symptoms and be absorbed into the tissues below (dermal absorption). Sub-dermal absorption, which is the preparation used to deliver medications such as nicotine and lidocaine, targets the bloodstream.
An explanation of dermal absorption and the three different dermal pathways as stated by the National Institute for Occupational Health and Safety is shown below.
Dermal absorption is the transport of a chemical from the outer surface of the skin both into the skin and into the body. Studies show that absorption of chemicals through the skin can occur without being noticed by the worker, and in some cases, may represent the most significant exposure pathway. Many commonly used chemicals in the workplace could potentially result in systemic toxicity if they penetrate through the skin (i.e. pesticides, organic solvents). These chemicals enter the bloodstream and cause health problems away from the site of entry.
The rate of dermal absorption depends largely on the outer layer of the skin called the stratum corneum (SC). The SC serves an important barrier function by keeping molecules from passing into and out of the skin, thus protecting the lower layers of skin. The extent of absorption is dependent on the following factors:
- Skin integrity (damaged vs. intact)
- Location of exposure (thickness and water content of stratum corneum; skin temperature)
- Physical and chemical properties of the hazardous substance
- Concentration of a chemical on the skin surface
- Duration of exposure
- The surface area of skin exposed to a hazardous substance
Research has revealed that skin absorption occurs via diffusion, the process whereby molecules spread from areas of high concentration to areas of low concentration. Three mechanisms by which chemicals diffuse into the skin have been proposed:
1. Intercellular lipid pathway (Figure 1)
2. Transcellular permeation (Figure 2)
3. Through the appendages (Figure 3)
Figure 1: Intercellular lipid pathway
As shown in Figure 1, the stratum corneum consists of cells known as corneocytes. The spaces between the corneocytes are filled with substances such as fats, oils, or waxes known as lipids. Some chemicals can penetrate through these lipid-filled intercellular spaces through diffusion.
Figure 2: Transcellular permeation
As shown in Figure 2, another pathway for chemicals to be absorbed into and through the skin is transcellular, or cell-to-cell, permeation whereby molecules diffuse directly through the corneocytes.
Figure 3: Through the appendages (hair follicles, glands)
As shown in Figure 3, the third pathway for diffusion of chemicals into and through the skin is skin appendages (i.e., hair follicles and glands). This pathway is usually insignificant because the surface area of the appendages is very small compared to the total skin area. However, very slowly permeating chemicals may employ this pathway during the initial stage of absorption.
Because there are three separate pathways through the skin, topical medications can come in many different forms, such as liniments, oils, salves, creams and ointments. The big difference is how the medication and carrying agents are arranged to optimize the efficacy of each formulation based on the dermal pathway it will use. The active ingredients used for the topical relief of pain fall into two broad categories, natural remedies and medicinal remedies.
Nonsteroidal Anti-inflammatory Drugs or NSAIDs are the medicine category and the topical NSAID formulations containing diclofenac, ibuprofen and ketoprofen are the most effective. The topical formulations of these drugs is a more widely accepted option as it avoids the gastrointestinal upset and bleeding that accompany their oral counterparts.
Capsaicin is the active ingredient in chili peppers and it gives that “burning sensation” to the topical pain creams that use it. The thought has always been that the burning or warming is the part of capsaicin that relieves the discomfort but the actual mechanics behind it are a bit more complex. Capsaicin activates nerve neurons to the point of overload which, after a short time, actually shuts them down.
Menthol is the exact opposite of capsaicin burning sensation and gives topical pain relief cream a cooling sensation. Like capsaicin, it is not an actual cooling of the skin that relieves the symptom, the menthol actually attaches to the neuronal receptor and sends a cooling signal to the brain.
Methyl Salicylate is not a medicine perse and it was originally thought that it was only used to add a wintergreen scent and subsequent cooling sensation to topicals however, once absorbed and metabolized in the body, it turns into salicylic acid. Salicylic acid is a sister to acetylsalicylic acid or Aspirin which is very well known for its pain suppression and anti-inflammatory properties.
Now that we understand the function of pain, the pathways that need to be taken by topicals to get to the site and the types of medications used to kill or numb the condition, we can look at how they are used to alleviate the symptoms caused by certain ailments. Let’s start with the use of topicals to relieve the pain of shingles. Shingles are a sore, blistering rash that is caused by the chickenpox virus, that has laid dormant under the surface of the skin until triggered to reemerge. Not only are the blisters painful, the itch that accompanies them is quite annoying as well. In this example, any topical ointment or cream that would be applied to relieve that pain, would also contain an anti-itch or numbing component. Topical pain relief for shingles generally comes from specially formulated medications such as “topical acyclovir 5% cream, lidocaine, and capsaicin.” Another good topical reliever for shingles is calamine lotion, applied as per the package instructions. Shingles is an obvious candidate for a topical remedy, as it manifests directly on the skin and a topical pain relief cream makes sense.
Other ailments like arthritis are more likely to lead suffers to strong over the counter analgesics and opioids to dissipate the pain but there are a great many topical pain creams for arthritis pain that work just as well. According to Kathee de Falla, PharmD, “It is easy to feel overwhelmed by the number of topical creams, balms, gels, patches, and sprays available to treat arthritis pain. Knowing about these products’ active ingredients and relative effectiveness can help people select the ones best suited for them.
Many topicals for arthritis are sold over-the-counter, without a prescription, while certain other topical products require a physician’s prescription.
Regardless of how they are applied to skin, most topical pain cream for arthritis fall into these categories:
- Counterirritants, which distract from pain
- Salicylates, which have mild anti-inflammatory effects
- Capsaicin products, which may have a role in blocking pain signals
- Lidocaine products, which work as local anesthetics
Over-the-counter topical pain relief products for arthritis are applied to the skin over the arthritic joint and tend to provide modest, local pain relief.
In the US, the most commonly prescribed topical pain relievers for arthritis include:
- Non-steroidal anti-inflammatory drugs, or NSAIDs (e.g. Voltaren Gel)
- Concentrated topical lidocaine products, including 5% lidocaine patches (e.g. Lidoderm Patches)
Topical NSAIDs may offer some advantages over their oral medication counterparts, such as reduced gastrointestinal side effects; however, they still carry risks and can interact with some oral medications.”
If you aren’t quite ready for OTC topical pain creams there are a great many natural pain remedies that are also topicals or can be made into topical pain relief oils. Lavender oil, peppermint oil, rosemary oil, cloves, cayenne powder and ginger all have proven pain fighting properties. On their own or together, they would make a good natural pain remedy alternative to Oral NSAIDs.
As a closing note for dog owners, the science of topical pain medications has recently been applied to canines. Owners that have canine family members who suffer from arthritis, sore joints, over activity and old age have a topical pain relief option for dogs. As with their human formulations, topical pain relief for dogs targets inflamed and aggravated nerve endings and pain receptors. The idea behind the products is the same, bring down the inflammation and mask or eliminate the pain so your dog can live a happier life. A quick online search will put you in touch with a list of companies currently producing topical products for dogs.