A rash is an area of irritated or swollen skin. Often, rashes are unidentifiable and some variation of normal. For example, scratching one's arm causes it to turn red (which is caused by mast cells releasing chemicals into the local area), but that's completely normal.

Rarity: Common

Top Symptoms: knee redness

Symptoms that always occur with non-specific knee rash: knee redness

Urgency: Wait and watch

Allergic contact dermatitis of the knee

Allergic contact dermatitis is a condition in which the skin becomes irritated and inflamed following physical contact with an allergen. Common products known to cause allergic dermatitis include plants, metals, soap, fragrance, and cosmetics.

Rarity: Common

Top Symptoms: knee redness, knee itch, scabbed area of the knee

Symptoms that always occur with allergic contact dermatitis of the knee: knee redness

Urgency: Self-treatment

Knee redness questionnaire

Use our free symptom checker to find out what's causing your redness.

Knee redness symptom checker

Skin infection of the knee

Cellulitis is an infection of the skin and tissues underneath it. It is most commonly caused by Group A strep and typically enters the body through a break in the skin.

Rarity: Uncommon

Top Symptoms: fever, knee pain, knee redness, knee injury, painful knee swelling

Symptoms that always occur with skin infection of the knee: knee redness, area of skin redness

Urgency: Primary care doctor

Insect bite from a chigger

Chiggers are mites that feed on humans and animals only while they are larvae, or their infant form. People can contract chiggers when they contact infected grass. Chiggers feed for three to four days on a piece of skin, and secrete a fluid that causes intense itching.

Rarity: Rare

Top Symptoms: lower leg itch, lower leg redness, knee itch, ankle itch, ankle redness

Urgency: Phone call or in-person visit

Necrotizing fasciitis of the leg

Necrotizing fasciitis is a potentially life threatening skin condition stemming from the infection of a wound or injury. If left untreated, it can spread to body parts surrounding the infection changing the color of the skin and degrading the tissue underneath. This can result in muscle, tissue or limb loss and a severe body-wide response to the infection.

Rarity: Ultra rare

Top Symptoms: nausea, diarrhea, vomiting, fever, chills

Symptoms that always occur with necrotizing fasciitis of the leg: leg skin changes

Urgency: Hospital emergency room

Lyme disease

Lyme disease is a bacterial illness transmitted through the bite of the deer tick (black-legged tick) after it has been attached for at least 36-48 hours. These may be tiny, immature ticks that are difficult to see, often attaching in a place on the body where hair grows.

The disease does not spread through casual contact, either between humans or between humans and pets.

Early symptoms include fever, chills, headache, and body aches. There may be a rash around the tick bite, which sometimes enlarges to form a clear circle around the bite.

Later symptoms are severe with headaches, neck stiffness, further rashes, facial drooping (palsy,) and joint pain and swelling. This is a medical emergency. Take the patient to the emergency room or call 9-1-1.

Untreated Lyme disease in a pregnant woman can lead to stillbirth, but antibiotics will usually prevent this.

Diagnosis is made through symptoms as well as a blood test.

Treatment consists of oral antibiotics in most cases, though severe cases may require IV antibiotics.

Rarity: Ultra rare

Top Symptoms: fatigue, headache, irritability, muscle aches, loss of appetite

Urgency: Primary care doctor

Knee redness questionnaire

Use our free symptom checker to find out what's causing your redness.

Knee redness symptom checker

Questions your doctor may ask about knee redness

To diagnose this condition, your doctor would likely ask the following questions:

Do you have a rash?
Is the red area flaky and rough to the touch?
The redness affects one knee or both knees?
Did your symptoms start after you were exposed to nickel (commonly found in jean snaps, metal pens, paper clips, cigarettes, etc.)?

Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.

Knee redness symptom checker statistics

People who have experienced knee redness have also experienced:

9% Knee Pain
8% Lower Leg Redness
5% Upper Leg Redness

People who have experienced knee redness were most often matched with:

80% Skin Infection Of The Knee
20% Allergic Contact Dermatitis Of The Knee

People who have experienced knee redness had symptoms persist for:

48% Less than a day
26% Over a month
20% Less than a week

Source: Aggregated and anonymized results from Buoy Assistant.

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