Allergic Reactions

Few disorders encompass such a wide presentation and severity of symptoms as allergic reactions. Many explorers will either experience allergic symptoms of their own or travel in the company of someone who does. Food allergies, allergic rhinitis, drug allergies, toxicodendron dermatitis, and life threatening anaphylaxis are several of the more important presentations that wilderness explorers may encounter, and thus, a basic understanding of the pathophysiology, presentation, and treatment of each should be acquired by at least one expedition member.

Pathophysiology

The body’s immune system serves to protect it from foreign invaders like bacteria. An allergic reaction occurs when the immune system mistakes harmless environmental particles (called antigens) as foreign and develops small particles called IgE that are capable of recognizing the antigen if and when it is encountered in the future. When this occurs, IgE triggers the release of histamine and other chemicals causing inflammation in the skin, airways, intestines, and blood vessels. Thus, in order to develop a true allergy, one must usually first be exposed, then develop an overactive response, and then be re-exposed to the same antigen at some point in the future. With repeated exposure, the reaction is typically amplified.

Food Allergies

Allergies to certain foods (peanuts, shellfish, etc) typically occur within 5 minutes to two hours after ingestion. Food allergies range from mild (skin rashes and runny nose) to severe (wheezing, oral swelling, nausea, vomiting, and low blood pressure). Annoying skin manifestations include hives, a rash consisting of red, blotchy, itchy areas which can form anywhere on the skin surface. Hives are migratory: mark the rash’s edge with a marker and in 20-30 minutes, the rash will have moved, expanded, changed shape, or disappeared all together. It’s reasonable to take diphenhydramine (Benadryl) at the first onset of food allergy symptoms, but because these reactions can become life threatening, future avoidance and allergy testing are paramount. More serious reactions such as angioedema (fluid leaking through blood vessels to cause marked swelling) of the lips or oral cavity, gastrointestinal upset, and shock (low blood pressure) should prompt immediate treatment with oral diphenhydramine (Benadryl) and injectable epinephrine if previously prescribed by a physician, and expeditious evacuation to definitive medical care. Many other bad reactions (food poisoning, lactose intolerance, peptic ulcer disease, etc.) are frequently mislabeled as allergies, and an upset stomach from Baja fish tacos and Corona should not dissuade you from trying the combination again.

An Epi-Pen contains epinephrine and can be a life saving addition to a wilderness first aid kit.

Allergic Rhinitis

While diphenhydramine (Benadryl) can be sedating and cause dry mouth, it’s effective for seasonal allergies.

Allergic rhinitis is a constellation of symptoms including rhinorrhea (runny nose), itching, sneezing, and nasal congestion. Much advice exists on how to avoid allergic rhinitis triggers; however, most explorers generally find avoidance unpractical and symptom relief must be attained through histamine blocking medication. First generation anti-histamines such as diphenhydramine (Benadryl) work well but easily cross into the brain where they cause side effects like sedation. Second generation anti-histamines, such as loratadine (Claritin) and cetirizine (Zyrtec), work equally well but do not cross into the brain and therefore do not cause sedation. They are the antihistamine of choice for vehicle dependent explorers who must stay awake while at the wheel. Those whose symptoms include nasal congestion may also benefit from pseudoephedrine, an oral medication that constricts the sinus’ blood vessels and decreases swelling caused by histamine. Pseudoephedrine is available by itself or in combination with antihistamines (Zyrtec-D, the “D” indicating that it also contains a “decongestant”). Beware though, as pseudoephedrine can cause a temporary increase in blood pressure. Particularly nasty nasal symptoms are most effectively treated with intranasal steroid sprays that have relatively few side effects but are available only by prescription.

Drug Reactions

Drug reactions can be non-allergic (nausea, sedation, interaction with other medications) or allergic. True drug allergies can be life threatening and result in the typical histamine mediated response in addition to other more complex presentations such as anemia (low blood count) and fevers. The most typical culprits are antibiotics such as penicillin and sulfa-containing medications. It’s difficult to predict who will have a drug reaction, and care should be avoided when taking a new medication for the first time when in a remote wilderness setting.

Toxicodendron Dermatitis

Toxicodendron dermatitis to the Anacardiaceae family (poison oak, ivy, and sumac) results from an abnormal immune response to the plants’ urushiol oil. The resulting rash is extremely pruritic (itchy) and erythematous (red). Typically the rash develops small fluid filled blisters arranged in linear, streak-like patterns: telltale signs of where the plant brushed against the skin while hiking or doing yard work. The rash develops gradually between four hours and 21 days after exposure and sometimes tricks the patient into believing the rash is “spreading.” The fluid released from ruptured blisters does not spread the rash; however, urushiol oil remaining on un-washed clothing can certainly cause spreading and affect others. Wash all clothes and skin with soap! Left untreated, the rash resolves in one to three weeks. Histamine plays little to no part in this particular allergy; therefore, antihistamines like Benadryl are not very helpful and owe their anti-itch properties more to the sedation side effects than actual histamine blockade. Topical steroids (1% hydrocortisone cream, available over-the-counter) are the treatment of choice for itchy symptoms, but once blisters appear, the reaction is pretty much in full swing and will run its course regardless of attempted therapy. Higher potency topical steroids are occasionally prescribed, but the risks sometimes outweigh the actual benefits. Severe dermatitis of the face or genitals may necessitate treatment with oral steroids, but no studies have determined the proper dose or duration of treatment. Outdoorsmen would be better off studying photos of the offending plants in addition to memorizing the old adage “leaves of three, quickly flee; berries of white, take flight!”

Poison Ivy: Leaves of three, quickly flee!

Life-threatening Anaphylaxis

Few things scare a first responder as much as anaphylaxis (life-threatening allergy) encountered in a wilderness setting. Victims can become overcome so quickly by airway swelling, vomiting, hives, and shock, that they are rendered unable to treat themselves and the duty then falls upon teammates to administer epinephrine (adrenaline). If you or an expedition member has had severe, life threatening allergies (most typically to foods, medications, and insect stings), the entire team must be informed and properly trained to administer an auto-injector, a pen-sized epinephrine-containing device. The wrong time to learn about auto-injectors is when your teammate is in extremis. “Dummy” auto-injectors are available for training and a trial run can drastically reduce the odds of injecting your own thumb when using the device for the first time. Epinephrine’s effects are short lived and often multiple injections are required, thus, any signs of anaphylaxis require prompt treatment and evacuation. The carriage of epinephrine auto-injectors by wilderness first responders is a topic of much current debate, as epinephrine is a prescription drug with dangerous side effects. Some states consider it negligence for laypersons to administer the drug. Malpractice insurance excludes coverage of an illegal act, further muddying the waters for physicians who provide emergency care in states or countries where no license is held. For those interested in learning about epinephrine administration in the wilderness setting, advanced training can be obtained from multiple sources including the National Outdoor Leadership School (NOLS), the Wilderness Medical Society (WMS), and Remote Medical International (RMI).

For unknown reasons, allergies are becoming increasingly prevalent in today’s society, making your odds of dealing with them while on expedition increasingly more likely. This month, check your first aide kit and ensure it contains a few tablets of non-sedating antihistamine.  If you’re traveling to areas where plants of the Anacardiaceae family reside, ensure everyone in the group knows how to identify the offending plant, pack some hydrocortisone ointment, and take a plastic bag into which you could potentially place contaminated clothing until clothes washing facilities are available. Most importantly, share your pertinent medical history with the group before you embark and review the medical contingency plan, including identification and treatment of any known life-threatening disorders like anaphylaxis.  Doctor’s orders!