Bleach is ineffective on porous surfaces like grout or drywall as it only bleaches the surface, leaving the root structure intact. For a small patch, use a dedicated EPA-approved fungicidal cleaner, scrubbing thoroughly and allowing it to dwell on the surface. However, if it has already returned after bleaching, the growth is likely more extensive behind the tiles or within the wall.

Permanent removal requires addressing the moisture source. Ensure your bathroom’s exhaust fan is functioning properly and runs during and for 30 minutes after showers. Wipe down wet surfaces and fix any leaking pipes or seals. For persistent humidity, a dehumidifier can help.

Given the recurrence and the health symptoms, a professional inspection is advised. They can identify the full extent of the hidden moisture and mold growth, which is common in our climate. Remediation often involves removing and replacing compromised sealants or wall materials to ensure it’s truly resolved. A company with its own microbiology lab can provide definitive identification and post-remediation verification testing to confirm the space is safe.