Unhoused street medicine: immersion (trench) foot, wound care, and medication storage¶

When you are living outdoors, sleeping in a tent or vehicle, or staying in congregate shelters, minor medical problems that are easy to manage in a house with running water and a refrigerator can escalate into life- or limb-threatening emergencies in 48 hours. Walking 15 kilometers (9 miles) a day in rain-soaked shoes without taking your boots off at night causes non-freezing cold injury (immersion or "trench" foot), a scraped shin or blister exposed to street dirt turns into rapidly spreading bacterial cellulitis, and extreme summer heat or winter frost destroys unrefrigerated insulin and rescue inhalers.

Street medicine physicians and wilderness first responders emphasize that protecting your feet, cleaning wounds early with potable water, recognizing the red-flag signs of sepsis, and using water-activated evaporative cooling pouches or body-heat insulation for critical medications prevents hospitalizations and amputations.

Do this now¶

1. Check for emergency red-flag symptoms of sepsis or deep tissue infection first. If you or someone in your camp develops a warm, expanding red skin infection accompanied by fever or chills, confusion, dizziness, rapid breathing, purple/black skin blisters, severe pain out of proportion to the wound, or red streaks spreading up an arm or leg, call your local emergency numbers (911 in the United States and Canada, 112 across the European Union, 999 in the United Kingdom) immediately. Hospital emergency departments are legally required to evaluate and stabilize life-threatening medical emergencies regardless of your ability to pay or whether you have ID or insurance.
2. Take your shoes and wet socks off for at least 6 to 8 continuous hours every single night. Never sleep in wet boots or damp socks. Even when outside temperatures are well above freezing, up to 15 degrees Celsius (60 degrees Fahrenheit), keeping your feet trapped inside wet, tight footwear for 24 to 48 hours constricts blood vessels, kills foot nerves, and causes immersion (trench) foot.
3. Never warm numb, pale, or frostbitten/immersion-damaged feet right next to a camp stove, fire, or car heater vent. Because cold-damaged or diabetic feet have numb nerves, you cannot feel when radiant heat is burning your skin, and rapid high-heat rewarming of immersion foot triggers severe tissue swelling, blistering, and unbearable burning nerve pain (hyperemia). Warm cold feet gently at room temperature or against a companion's warm torso/armpits.
4. Trace the outer border of any red skin infection with a ballpoint pen and write the time. If a cut, bug bite, or leg ulcer turns red, hot, and swollen, draw a pen line right along the outer edge of the redness. If the redness spreads past your pen line within 2 to 4 hours, you have an active bacterial cellulitis infection that requires prescription oral or IV antibiotics from a street-medicine clinic or urgent care today.
5. Wash open cuts with clean bottled drinking water or sterile saline, never use hydrogen peroxide or rubbing alcohol inside an open wound. Pouring full-strength hydrogen peroxide or isopropyl alcohol into a raw wound kills the healthy new white blood cells and skin cells trying to heal the cut. Flush dirt out using a strong stream of potable water (pierce a pinhole in the cap of a sealed water bottle to make a high-pressure irrigation squirt bottle), pat dry, apply plain petroleum jelly (Vaseline) or antibiotic ointment, and keep it covered.
6. Protect insulin and epinephrine from freezing against ice packs in winter and baking in backpacks in summer. In freezing weather, carry your active insulin pen and asthma inhaler in an inside shirt pocket right against your warm skin so it cannot freeze solid (frozen insulin is permanently destroyed and must never be injected). In summer heat above 30 degrees Celsius (86 degrees Fahrenheit), store insulin inside a water-activated evaporative cooling pouch (FRIO wallet) or shaded insulated thermos, never in a dark outside backpack pocket sitting in the sun.

Street medicine foot and wound triage flowchart¶

Use this clinical decision tree to evaluate foot pain, numbness, skin infections, and blisters in the field.

flowchart TD
    A["Foot pain, numbness, blister, or skin wound in the field"] --> B{"Are there systemic emergency red flags?"}
    B -->|"Fever/chills, confusion, red streaks, black tissue, or crackling gas under skin"| C["LIFE-THREATENING SEPSIS / NECROTIZING INFECTION: Call 911/112/999 or go to ER now"]
    B -->|"No systemic fever or confusion"| D{"What does the foot or wound look like?"}
    D -->|"Feet were wet/cold for 12+ hrs; skin is pale, wrinkled, numb, and waxy"| E["IMMERSION (TRENCH) FOOT: Remove wet boots/socks, pat dry gently, elevate, and warm slowly at room temp"]
    D -->|"Feet were below 0°C (32°F); skin is frozen hard, white/grey, and wooden"| F["FROSTBITE: Do NOT walk on frozen toes if refreezing is possible; seek hospital warm-water bath"]
    D -->|"Hot, swollen, tender, expanding red patch around a cut or bug bite"| G["CELLULITIS OR ABSCESS: Draw pen border around redness and visit Street Medicine / FQHC clinic for antibiotics"]
    D -->|"Fluid-filled friction blister or shallow scrape"| H["Leave intact blister roof UNPOPPED; pad with moleskin donut or wash cut with clean water + Vaseline"]

Immersion Foot ("Trench Foot") vs Frostbite: Prevention and Field Treatment¶

Immersion foot (historically called Trench Foot) is one of the most common and devastating conditions treated by street medicine teams in autumn, winter, and rainy spring weather.

Why you do NOT need freezing weather to lose toes to Immersion Foot¶

Unlike frostbite (which only happens when tissue literally freezes into ice crystals at temperatures below 0 degrees Celsius / 32 degrees Fahrenheit), immersion foot occurs at any cool, wet temperature between 0 and 15 degrees Celsius (32 and 60 degrees Fahrenheit) whenever your feet stay continuously damp inside constricting shoes or boots for 12 to 48+ hours.

When your feet are wet and cool, the body clamping down on blood vessels (vasoconstriction) starves the nerves, skin, and blood vessel walls in your feet of oxygen. Meanwhile, water-logged skin (maceration) breaks down its protective barrier, allowing fungi and bacteria on your socks to invade deep tissues.

Clinical comparison: Immersion Foot vs Frostbite vs Diabetic Neuropathy¶

The 5 Street-Medicine Rules to Prevent Immersion Foot¶

1. The "Sleep Socks vs Walking Socks" Rule: Always keep one pair of thick wool or synthetic fleece socks sealed inside a waterproof Ziploc freezer bag at the bottom of your pack, used strictly for sleeping. Even if you have to put damp walking socks back on in the morning to hike to a day shelter, taking off your boots and letting your bare feet air-dry inside dry sleeping socks for 7 hours every night resets the clock and prevents trench foot completely.
2. Choose Merino wool or synthetic polypropylene socks, refuse 100% cotton socks: When well-meaning outreach groups hand out white 100% cotton athletic socks, use them only in dry summer weather or as inner hand mittens. Cotton holds sweat against your skin like a wet towel. Ask outreach vans specifically for wool-blend or polyester/acrylic boot socks.
3. Dry damp walking socks inside your sleeping bag using body heat: When you take off damp (not mud-soaked) walking socks at night, flatten them out and tuck them inside your shirt against your chest or around your waist inside your sleeping bag, your body heat will dry them out by morning.
4. The Plastic Bread-Bag Vapor Barrier Trick (Emergency short-term use only): If your shoes or boots are completely soaked through with freezing slush and you have to walk 2 hours to a shelter with your last pair of dry socks, put your dry socks on first, slip a plastic grocery bag or bread bag over the dry sock, and step into the wet shoes. This keeps the icy outside puddle water from soaking your dry socks during the walk, but you must remove the plastic bags as soon as you stop walking so trapped sweat does not macerate your skin.
5. Never lace wet boots tightly: Swollen cold feet laced tightly inside narrow boots lose remaining arterial blood flow. Loosen your laces by one notch and wiggle your toes for 60 seconds every 20 minutes to pump warm blood down to the tips.

Field Wound Care: Treating blisters, cuts, abscesses, and cellulitis without a bathroom¶

When living rough, minor skin breaks are constantly exposed to Staphylococcus aureus (including MRSA, methicillin-resistant Staph aureus) and Streptococcus bacteria. Follow these street-medicine wound protocols:

1. How to make a High-Pressure Sterile Irrigation Bottle from a 1-dollar water bottle¶

In wilderness and street medicine, the #1 factor that prevents wound infection is not expensive antibiotic cream, it is high-pressure mechanical water irrigation (flushing bacteria and grit out of the cut).

• Take a brand-new, sealed bottle of plain drinking water (never flavor-added or sparkling water).
• Heat the tip of a safety pin or paperclip (or use the point of a clean knife) to poke a single 1- to 2-millimeter pinhole right in the center of the plastic screw cap.
• Squeeze the bottle firmly with both hands, aiming the high-pressure stream at a 45-degree angle across the open cut using at least 250 to 500 milliliters (1 to 2 cups) of water until zero visible dirt remains.

2. Why plain White Petrolatum (Vaseline) beats Triple-Antibiotic Ointment for routine cuts¶

Dermatologists and street medicine clinics increasingly stock single-use packets of plain white petrolatum (Vaseline) or Aquaphor alongside or instead of over-the-counter triple-antibiotic ointment (neomycin / polymyxin B / bacitracin):

• Up to 10 to 15 percent of people develop an allergic contact dermatitis reaction to Neomycin after several days of use, causing the skin around the cut to turn red, itchy, and blistered, which looks just like a worsening bacterial infection.
• Keeping a clean, irrigated cut coated with a thin layer of plain petroleum jelly under a clean bandage keeps the wound bed moist so skin cells migrate across twice as fast without scabbing, cracking, or causing antibiotic-allergy rashes.

3. Friction Blisters: When to leave them intact vs how to drain a giant crippling foot blister¶

Walking 10+ kilometers a day with a heavy backpack causes painful fluid blisters on the heels and balls of the feet:

• If the blister is small (< 2 cm / 0.8 inches) and intact: DO NOT POP IT. The unbroken dome of skin over a blister is the most sterile biological bandage on earth. Cut a piece of moleskin, felt, or folded duct tape/gauze into a "donut" shape (with a hole cut in the center right over the blister dome) and tape it around the blister so your shoe rubs on the surrounding pad instead of crushing the blister.
• If a large tension blister on the sole of your foot is about to burst on its own because you have no choice but to walk: Rather than letting your dirty sock rip the roof off the blister inside your boot, drain it cleanly:
  1. Wash the blister and your hands thoroughly with soap and potable water, and wipe the blister edge with a 70% alcohol prep pad or povidone-iodine wipe.
  2. Sterilize a sewing needle or safety pin with an alcohol pad (do not use an open match flame if it leaves black carbon soot on the needle unless you wipe the soot off with alcohol).
  3. Poke two tiny side-entry holes right at the base edge of the blister parallel to the foot sole, gently press the clear fluid out with clean gauze, LEAVE THE SKIN ROOF COMPLETELY IN PLACE OVER THE BLISTER BED, coat with Vaseline, and cover securely with a hydrocolloid blister plaster or gauze taped down with cloth athletic tape (or duct tape over a square of gauze).

4. Recognizing Cellulitis, MRSA Abscesses ("Spider Bites"), and Necrotizing Infections¶

Outdoors and in shelters, people frequently point to a painful, swollen, red boil oozing pus on their leg or arm and say, "A spider bit me in my tent last night." In clinical reality, 95 percent of suspected "spider bites" in camps and shelters are actually community-acquired MRSA (Staphylococcus aureus) bacterial skin abscesses.

How to store Insulin, Inhalers, and Epinephrine without a refrigerator¶

If you have diabetes, asthma/COPD, severe allergies, or take daily psychiatric or heart medications while unhoused, extreme temperatures and theft are constant threats. For power-outage storage rules at home, see our cold-chain medications guide; when living outdoors or in a vehicle, follow these specialized street-medicine rules:

Preventing shelter & camp skin infestations: Scabies, Body Lice, and Trench Fever¶

Crowded overnight shelters, shared blankets, and inability to launder clothing in hot water expose unhoused individuals to two major ectoparasites: Body Lice (Pediculus humanus corporis) and Scabies (Sarcoptes scabiei).

1. Body Lice vs Head Lice (Why body lice live in your clothes, not your hair):
   • Unlike head lice, body lice do NOT live on your skin or hair, they live and glue their eggs (nits) right inside the stitched fabric seams of your underwear, waistband, collar, and thermal base layers, crawling onto your skin only to feed and causing intense itching and scratch infections (as well as transmitting bacterial Bartonella quintana Trench Fever).
   • How to eradicate body lice in one afternoon: You do not even need prescription lotion for most body lice if you can wash or heat-treat your clothes. Sealing infested clothing, blankets, and sleeping bags inside a commercial laundromat clothes dryer on HIGH HEAT (> 55°C / 130°F) for 30 to 40 minutes kills 100 percent of adult body lice and their eggs inside the seams. If you cannot wash your clothes, ask a street medicine team for a clean clothing swap and a single dose of 1% permethrin cream or oral ivermectin.
2. Scabies (The night-itching web-space rash):
   • Caused by microscopic mites that burrow into the top layer of skin, especially between the fingers (web spaces), on the insides of the wrists, around the beltline, and in the armpits, causing tiny red bumps and wavy 5-millimeter burrow lines that itch fiercely at night when you warm up under blankets.
   • Treatment: Requires prescription 5% Permethrin cream (applied from the neck down to the soles of the feet for 8 to 14 hours overnight, then repeated in 7 days) or two doses of oral Ivermectin tablets (which street medicine doctors often prefer when a patient has no private shower to wash off full-body cream) plus heat-drying or bagging your clothing in sealed plastic bags for 72 hours (scabies mites starve to death off human skin within 3 days).

Frequently asked questions¶

Sources checked¶

• Street Medicine Institute (streetmedicine.org) and National Health Care for the Homeless Council (nhchc.org, United States): Clinical Guidelines for Street Medicine, lower-extremity immersion foot and wound care in unsheltered populations, and chronic disease management without housing.
• Centers for Disease Control and Prevention (CDC, United States): Trench Foot (Immersion Foot) Prevention and Treatment Guidelines, community-associated MRSA skin infection triage, and Emergency Wound Care After a Natural Disaster.
• Wilderness Medical Society (WMS): Clinical Practice Guidelines for the Prevention and Treatment of Frostbite and Non-Freezing Cold Injuries (Immersion Foot) and field wound irrigation pressures.
• United States Food and Drug Administration (US FDA) and American Diabetes Association (ADA): Information Regarding Insulin Storage and Switching Between Products in an Emergency (28-day room-temperature stability, freezing ruin hazard, and evaporative cooling guidance).
• National Health Service (NHS, United Kingdom) and Faculty for Homeless and Inclusion Health (United Kingdom): Clinical standards for street outreach wound care, trench foot, scabies/ectoparasite protocols, and free emergency care access.
• Centers for Medicare & Medicaid Services (CMS, United States): Emergency Medical Treatment and Labor Act (EMTALA, 42 U.S.C. 1395dd) patient rights guaranteeing emergency hospital stabilization regardless of insurance, ID, or ability to pay.

Related guides¶

• Unhoused survival and extreme weather triage
• Hypothermia and frostbite
• Sepsis and septic shock
• Cold-chain medications in power outage