If you live or work in San Ysidro, you probably know the smell: a heavy, rotten-egg odor that drifts in from the Tijuana River Valley, often at its worst after dark. Headaches, nausea, irritated eyes and a scratchy cough are among the most common sewage odor symptoms neighbors describe. Here is what causes the odor, who needs extra care, how to protect your home, and when to walk in or call 911.
What Causes the Odor and Why It Matters
The smell comes mainly from hydrogen sulfide, a colorless gas released as untreated wastewater breaks down. The Agency for Toxic Substances and Disease Registry (ATSDR) notes that people can smell it at very low levels and that, because it is heavier than air, exposure risk is greater at ground level and in enclosed spaces.
In a health consultation released for public comment, ATSDR reviewed outdoor air data from four monitoring sites in the valley. It concluded that hydrogen sulfide at one site, and likely a second at Berry Elementary School in Nestor, reached levels for short periods that could harm health, which it classifies as a public health hazard. Possible effects include headaches, a dry nose and throat, and possibly difficulty breathing in sensitive people. Longer exposures (14 days or more) are not expected to add effects beyond those short spikes, although odor-related symptoms can continue.
In a door-to-door CDC and County survey of South Bay households, known as a CASPER, 69 percent of households said at least one member had symptoms from the sewage crisis. Of those who could smell sewage, nearly 70 percent said it was strongest at night. For cross-border workers who leave before dawn or come home late, that timing matters.
Sewage Odor Symptoms Linked to Hydrogen Sulfide
Everyone reacts differently. The County of San Diego explains that the effect depends on how much gas is present, how sensitive you are, how active you are and how long you are exposed. Smelling the odor does not always mean it will make you sick. When symptoms do appear, the County and ATSDR list:
- Headaches
- Nausea or an upset stomach
- Eye, nose and throat irritation, nasal congestion, hoarseness or a sore throat
- Cough, chest tightness or shortness of breath
- Tiredness, poor memory or balance problems
- Stress or annoyance
CASPER households reported headache, nausea or upset stomach, cough and an irritated throat most often, which is why so many neighbors connect the rotten egg smell with a headache and nausea.
The reassuring part: the San Diego County Air Pollution Control District (APCD) says sewage odor symptoms are expected to resolve when the odor goes away or when you leave the area, and that there is no scientific evidence the odor causes lasting health effects. Longer-term Tijuana River sewage health effects are still being studied, including a County partnership with UC San Diego.
One caution: your nose is not a reliable alarm. OSHA warns that at high concentrations people can lose the ability to smell hydrogen sulfide within minutes. Keep children out of drainage channels, culverts and storm drains, where the heavier gas can collect.
Who Is Most Sensitive: Asthma, Kids and Seniors
The County and APCD both say symptoms can be more severe or more frequent in people with asthma, chronic obstructive pulmonary disease (COPD) or heart disease. OSHA notes that hydrogen sulfide can narrow the airways in some people with asthma.
For children, the evidence is thinner. ATSDR says there is very little information on how hydrogen sulfide affects children. The County advises that children with breathing or heart conditions are more vulnerable and may need extra precautions, such as less outdoor play when the odor is strong.
Older adults with heart or lung disease fall into the same higher-risk group, and APCD's free air purifier program gives priority consideration to households with children and adults over 65. If anyone at home has asthma or COPD, keep their rescue medication within easy reach whenever odors are present.
Steps to Protect Your Home
County public health guidance recommends these steps when the odor is bothersome:
- Limit time outdoors when the smell is strong, especially strenuous activity.
- Keep doors and windows closed while odors are present, then air out your home once the air improves.
- Circulate indoor air with fans, or run air conditioning on recirculation mode.
- Use the right air purifier. A unit with a HEPA filter plus activated charcoal and potassium permanganate is particularly effective for hydrogen sulfide odors.
- Keep inhalers and other rescue medicines handy for anyone with asthma, COPD or another chronic lung condition.
APCD's Air Improvement Relief Effort (AIRE) Program offers free air purifiers to eligible households, including most of San Ysidro, while supplies last. APCD also runs a hydrogen sulfide monitor at Fire Station 29 in San Ysidro, posts readings online, and offers email or text alerts when levels pass 30 parts per billion. Its community guidance is published in English and Spanish.
The strain is real as well: 59 percent of households in the County survey said their overall stress had increased. If worry or low mood feels overwhelming, call 988, the Suicide & Crisis Lifeline.
When to Walk In and When to Call 911
Call 911 or go to the nearest emergency room if:
- Breathing trouble comes on suddenly or makes it hard to talk (MedlinePlus)
- Someone stops breathing or loses consciousness
- Lips or face turn bluish, or there is drowsiness or confusion (MedlinePlus)
- Severe shortness of breath at rest, extreme difficulty breathing or a racing pulse
- Crushing, squeezing chest pressure, or pain that spreads to the jaw, left arm or between the shoulder blades (MedlinePlus)
These signs can have other causes, so do not wait to decide whether the smell is to blame.
Walk in for an exam if:
- A headache, nausea or eye and throat irritation lasts after the odor fades or after you leave the area
- A cough, wheeze or chest tightness keeps coming back
- An asthma flare needs more rescue medicine than your plan recommends
- You feel short of breath while talking or with light activity
- You are worried about your own health or your child's
At Palm Urgent Care, San Ysidro, 601 E San Ysidro Blvd #170, a clinician can evaluate your symptoms, examine your breathing and help decide on next steps, with lab testing available when symptoms suggest another cause. ATSDR notes that blood and urine tests for hydrogen sulfide cannot predict health effects, so a visit to urgent care in San Ysidro focuses on how you feel. Not sure which setting fits? Read our guide to urgent care vs. the emergency room.
Frequently Asked Questions
Can the sewage smell in San Ysidro make you sick?
It can cause short-term symptoms such as headaches, nausea, and eye, nose and throat irritation. APCD reports no scientific evidence of lasting effects from the odor, but ATSDR found short spikes at some valley sites reached levels that could harm health, so limit exposure when the smell is strong.
How long do hydrogen sulfide symptoms last?
The County of San Diego says symptoms should be short-term and typically resolve when the odor goes away or when you leave the area. If they persist, worsen or worry you, see a clinician.
What air purifier works best for sewage odor?
County guidance says a purifier with a HEPA filter, activated charcoal and potassium permanganate is particularly effective for hydrogen sulfide odors. Eligible San Ysidro households may get a free unit through the APCD AIRE Program.
Is sewage odor more dangerous for children or people with asthma?
People with asthma, COPD or heart disease may have stronger or more frequent symptoms. Research on children is limited, but the County advises extra precautions for children with breathing or heart conditions.
When should I go to the ER for sewage odor symptoms?
Call 911 for sudden or severe trouble breathing, bluish lips or face, confusion, loss of consciousness or crushing chest pain. Do not wait it out at home.
If the odor is affecting how you feel, visit the Palm Urgent Care San Ysidro location page for hours, directions and walk-in details, or reach us through the contact page.
This article is for general information and is not a substitute for medical advice from a licensed clinician.