If you searched “STF,” you most likely meant STI (sexually transmitted infection) or possibly a staph infection, since both are common health concerns people try to self-check. Many STIs cause no obvious symptoms at all, which means testing is the only reliable way to know for sure. Staph infections, on the other hand, almost always show visible skin changes. This guide covers both so you can figure out which one applies to you.
STI Symptoms Are Often Silent
The tricky thing about sexually transmitted infections is that many of them produce no symptoms, especially early on. You can carry and spread chlamydia, gonorrhea, HPV, or even HIV without feeling anything unusual. That’s why routine screening matters if you’re sexually active, particularly with new partners. Testing is the only way to be certain.
When symptoms do appear, they tend to follow patterns depending on the infection. Knowing what to look for can help you act faster.
Chlamydia and Gonorrhea
These two bacterial infections share a lot of overlap in how they show up. Both can cause painful or burning urination, unusual discharge from the penis or vagina, and pain in the lower abdomen or pelvis. Gonorrhea may also produce thick, cloudy, or bloody discharge and can cause painful, swollen testicles. Chlamydia sometimes triggers bleeding between periods in women or lower back pain.
Both infections can also affect the rectum and throat if transmitted through anal or oral sex, causing rectal pain, discharge, bleeding, or a sore throat. Many people with chlamydia or gonorrhea have zero symptoms for weeks or even months, which is why these infections spread so easily.
Genital Herpes and HPV
Herpes typically shows up as small red bumps, blisters, or open sores around the genitals, buttocks, or inner thighs. These are often accompanied by pain, itching, or a pressure sensation in the lower abdomen. Outbreaks come and go, and the first one is usually the worst. Between outbreaks, you may have no visible signs at all.
HPV (human papillomavirus) often causes no symptoms whatsoever. When it does, you might notice a small bump or cluster of bumps in the genital area that can take on a cauliflower-like shape. Some strains of HPV cause genital warts, while others increase cancer risk without ever producing visible warts. Itching, discomfort, and bleeding during sex are possible but not universal.
HIV and Hepatitis
Early HIV symptoms can mimic the flu: fever, chills, headache, muscle aches, sore throat, swollen lymph glands, rash, fatigue, and night sweats. These appear within a few weeks of infection and then fade, sometimes for years. During the chronic middle stage, you might experience ongoing swollen lymph nodes, diarrhea, weight loss, fever, and cough. Without treatment, HIV can progress to AIDS, which brings severe weight loss, recurring fevers, soaking night sweats, and vulnerability to serious infections like pneumonia.
Hepatitis B and C can cause fatigue, nausea, vomiting, loss of appetite, fever, dark urine, and pain on the right side of your abdomen beneath the ribs (where your liver sits). Some people carry hepatitis for years without obvious symptoms while the virus slowly damages the liver.
Trichomoniasis
This parasitic infection is one of the most common STIs and is also one of the easiest to miss. Women may notice a clear, white, greenish, or yellowish vaginal discharge with a strong fishy odor, along with itching, burning, or soreness. Men sometimes experience itching or irritation inside the penis and painful urination, but many men have no symptoms at all.
If You Meant Staph Infection
Staph infections look very different from STIs. They almost always start on the skin and are caused by Staphylococcus bacteria entering through a cut, scrape, or hair follicle. The most common sign is a bump or sore that’s red (or purple or brown on darker skin), swollen, warm to the touch, and painful. It may be filled with pus or fluid.
Staph takes several forms. Folliculitis appears as pus-filled bumps around hair follicles that look like pimples but tend to be itchier and crust over. Boils are deeper pockets of pus, commonly found under the arms, around the groin, or on the buttocks. Impetigo shows up as sores on the face that burst and leave a yellowish crust. MRSA, the antibiotic-resistant form, often starts as a small red bump that looks like a pimple or spider bite but quickly becomes a hard, painful, deep abscess.
When a Staph Infection Gets Serious
A staph infection that stays on the skin surface is usually manageable. The concern is when it spreads deeper. Signs of progression include skin that feels hard and swollen, blisters that break open and leave raw surfaces resembling burns, and spreading areas of discoloration. If you develop a fever alongside a skin infection, or if symptoms haven’t improved within 48 hours, that’s a signal to get medical attention promptly.
Left untreated, staph infections can enter the bloodstream and cause pneumonia, surgical site infections, bloodstream infections, or sepsis. Red streaks radiating outward from a wound, rapidly spreading redness, or high fever with a skin infection are all signs that the infection may be moving beyond the skin.
How These Infections Are Diagnosed
STI testing typically involves a urine sample, blood draw, or swab of the affected area depending on the infection. Most results come back within a few days. Because many STIs overlap in symptoms, your provider will often test for several at once.
Staph infections are diagnosed by examining the skin and, when needed, taking a sample of pus, tissue, or fluid for lab culture. This culture identifies the exact bacteria and reveals whether it’s resistant to common antibiotics (as with MRSA). In more serious cases, imaging like CT scans or MRIs may be used to check for deeper complications, and an echocardiogram can evaluate whether the infection has reached the heart.
What Can Mimic a Staph Infection
Several other conditions look similar to staph on the skin. Insect bites, particularly spider bites, can produce the same red, swollen, painful bump. Drug reactions, gout flares, blood clots in the leg, and a chronic skin condition called stasis dermatitis (common in people with poor circulation) can all mimic cellulitis or staph. If an area of redness affects both legs equally, it’s almost certainly not an infection and more likely a circulation issue. One useful clue: staph infections tend to produce pus. If there’s no pus or drainage and the area isn’t getting worse over 24 to 48 hours, another cause may be more likely.