Swollen lymph node in the armpit (axillary node) after 3 months of vaginal sex is not a typical STI sign.
Most important point
STIs usually cause swollen lymph nodes in the groin (inguinal nodes), not in the armpit.
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STIs that can cause lymph node swelling
1)
HIV (Acute HIV phase)
Can cause generalized lymph node swelling (neck, armpit, groin)
But acute HIV symptoms usually come 2–6 weeks after exposure, not typically after 3 months.
Still, HIV test is necessary for confirmation, not symptoms.
2) Secondary Syphilis
Can cause generalized lymph node swelling.
Usually associated with rash (palms/soles), fever, sore throat, body aches.
3) Herpes
Lymph nodes usually swell in the groin, and there are typically painful genital ulcers/blisters.
4) Chlamydia / Gonorrhea
Mainly causes burning urination, discharge
Lymph nodes are usually groin, not armpit.
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Most common NON-STI causes of armpit lymph node
Skin infection / boil / shaving cut
Deodorant irritation
Fungal infection
Viral fever
Local infection in arm/hand
Tuberculosis (in some cases)
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What to do now (simple & correct)
Tests (recommended after 3 months exposure)
✅ HIV 4th generation test
✅ VDRL / RPR (Syphilis)
✅ HBsAg (Hepatitis B)
✅ Anti-HCV (Hepatitis C)
(Plus urine test for gonorrhea/chlamydia if discharge/burning exists)
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When to worry urgently
If lymph node is:
Hard, fixed
Increasing in size
More than 2–3 weeks
Associated with fever, weight loss, night sweats
Then physical examination + ultrasound is needed.
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Final Doctor’s Line (Clean)
A single armpit lymph node after 3 months is more likely due to local skin/viral causes than an STI, but HIV and syphilis testing should be done for confirmation.