That area looks most consistent with an irritated or mildly ingrown nail edge (early paronychia can also cause this pain), but I cannot diagnose from a photo alone.
What you can do now:
Soak toe in warm water 10–15 min, 2–3 times/day
Dry well after soaking
Apply a small amount of antibiotic ointment (if available) on the tender nail fold
Wear open-toe or wide shoes, avoid pressure on that side
Do not cut that corner deeply or dig under the nail
Pain relief: paracetamol/acetaminophen or ibuprofen if safe for the patient
Get urgent in-person care if any of these are present:
Spreading redness, swelling, warmth
Pus
Fever
Severe throbbing pain
Red streaking up the foot
Patient has diabetes, poor circulation, immune problems, or kidney disease
If pain is not improving in 24–48 hours, see a clinician/podiatrist. They may need drainage or partial nail edge treatment.
If you want, I can give a step-by-step home care plan for the next 3 days and explain exactly how to trim the nail safely after pain settles.
How can I treat at home as doctor
Home treatment for a painful nail edge (likely early ingrown nail/paronychia):
1) Clean and soak
Warm water + a little salt
Soak 15–20 min, 3–4 times/day
After soaking, dry completely
2) Topical medicine
Apply mupirocin or fusidic acid (if available) to the painful side, 2–3 times/day
If not available, use any basic antibiotic ointment
3) Reduce pressure from nail edge
After soaking (when nail is soft), gently lift the painful nail corner with clean cotton/floss
Place a tiny clean cotton wick under edge (only if tolerable)
Change daily after soak
Do not dig, cut deep corners, or tear skin
4) Footwear and protection
Open-toe sandals or wide toe-box shoes
Keep dry socks
Avoid running/trauma until better
5) Pain control
Paracetamol 500–1000 mg every 6–8 h as needed (max 3 g/day)
Or ibuprofen 400 mg every 8 h with food (avoid if ulcer/kidney disease/pregnancy/anticoagulants)
6) If mild inflammation only (no pus)
Short course hydrocortisone 1% around nail fold (not inside wound) once daily for 2–3 days can reduce inflammation
7) Watch daily
Need clinic procedure (possible partial nail avulsion) if:
Pus/abscess
Increasing redness/swelling after 48 hours
Severe pain preventing walking
Recurrent ingrown nail
8) Start oral antibiotics only if cellulitis/spreading infection
Examples (adult, if no allergy):
Cephalexin 500 mg every 6 h for 5–7 days
or
Flucloxacillin 500 mg every 6 h for 5–7 days
If MRSA risk/high prevalence, use local guideline alternative.