HEALTH AT WORK

Industrial Health

Farm Worker Getting Skin Blisters on Forearms After Handling Celery and Working in Sunlight

25 September 2026 · Health at Work · AI-assisted draft

Photo: Mark Stebnicki / Pexels

If you are a farm worker and you have noticed painful, burning blisters appearing on your forearms within a day or two of harvesting or handling celery in sunny conditions, you are not imagining a connection. The blisters are not caused by sunburn alone, and they are not an allergy in the conventional sense. They are the direct result of a well-documented occupational reaction called phytophotodermatitis — a chemical burn triggered when plant sap lands on skin that is then exposed to ultraviolet light. It is entirely predictable, entirely preventable, and far more serious than most farm operators realise until workers start presenting with it.

What Is Phytophotodermatitis and Why Does Celery Cause It

Phytophotodermatitis is a non-immunological reaction, which means it does not require prior sensitisation. Any worker whose skin contacts the responsible plant chemicals and is then exposed to UV light can develop it, on their very first day of exposure. The term breaks down simply: phyto (plant), photo (light), dermatitis (skin inflammation).

Celery — along with parsley, parsnip, fennel, hogweed, giant cow parsley, and citrus peel — contains naturally occurring chemical compounds called furanocoumarins, also referred to as psoralens. When these compounds soak into the outer layers of skin and are then struck by UVA radiation from sunlight, they trigger a phototoxic reaction that damages skin cells directly. The damage resembles a chemical burn more than a sunburn. The skin does not simply redden — it blisters, sometimes severely, and the blisters can take days to develop, which causes workers and supervisors to miss the link to the plant entirely.

Celery is a particularly high-risk crop because workers handle the stalks directly during harvesting, trimming, bunching, and packing. The sap is not contained — it splashes, drips, and smears across any exposed skin surface. Forearms are the most commonly affected area because workers reach into the crop repeatedly, sleeves are often rolled up in warm weather, and the forearms rest against cut stalks throughout the working day.

Who Is Most at Risk on the Farm

Any worker who handles celery or related crops with bare or partially bare forearms in outdoor conditions is at risk. The reaction does not discriminate by skin tone — phytophotodermatitis affects all skin types, though the subsequent hyperpigmentation (dark staining that can last months) may be more visible on lighter skin.

Risk increases significantly in the following situations:

• Harvesting during peak sunlight hours, typically between mid-morning and mid-afternoon
• Working in warm, humid weather when workers are more likely to roll up sleeves or remove protective layers
• Handling damaged or diseased celery, which releases more sap than healthy plants
• Workers who sweat heavily, as moisture on the skin accelerates furanocoumarin absorption
• Tasks involving cutting, trimming, or washing celery rather than simply transporting packaged product
• New or seasonal workers who have not been briefed on the hazard and do not recognise early warning signs

Supervisors should also note that the reaction can follow a lag of 24 to 72 hours. A worker who handles celery on a Tuesday morning and develops blisters on Thursday may not connect the two events, especially if they were not told to expect it. This delay is one of the most important facts to communicate during induction.

What the Reaction Looks Like: Early Signs and Later Stages

In the first hours after exposure, the affected skin may look entirely normal. Some workers notice a faint reddening or a sense of warmth on the forearm, but many notice nothing at all. This is the window where prevention is still possible — washing the skin thoroughly before UV exposure can reduce the reaction significantly.

Over the following 24 to 48 hours, the skin in the areas of sap contact begins to redden and swell. The pattern is often irregular and streaky, following the drip marks and splash patterns of the sap rather than appearing as a uniform band. This streaky or drip-mark pattern is a diagnostic clue that distinguishes phytophotodermatitis from other rashes.

By 48 to 72 hours, fluid-filled blisters appear on the reddened skin. These blisters can be large — several centimetres across — and are often painful or burning to the touch. They may burst and weep. In severe cases, workers find the forearms too tender to flex or grip. Affected workers have described the sensation as similar to a scald from hot liquid.

After the blisters heal, the skin typically develops dark brown hyperpigmentation in the exact pattern of the original sap contact. This discolouration can persist for weeks to months, even after the inflammation has resolved. It is not dangerous but can cause distress, particularly if workers are not warned to expect it.

Repeated episodes over a season can result in chronic skin damage and patches of irregular pigmentation. Workers who continue to be exposed without protection may develop increasingly severe reactions with each episode, as the skin becomes more sensitised to cumulative damage.

What Employers Are Responsible For Doing

Under occupational health regulations in most jurisdictions, employers have a duty to identify and control hazards that can cause harm to workers. Phytophotodermatitis from celery handling is a recognised occupational skin hazard, and the duty to manage it falls clearly on farm operators and growers.

This means the employer must:

• Carry out a skin hazard assessment for tasks involving celery and similar crops, identifying which workers are exposed and at what intensity
• Provide adequate personal protective equipment — specifically long-sleeved protective clothing that is resistant to liquid penetration, not simply ordinary cotton shirts that soak through rapidly
• Supply handwashing facilities close to the work area so that workers can remove sap from skin before sun exposure occurs
• Schedule high-contact tasks where possible to avoid peak UV hours, or rotate workers through shaded tasks to reduce cumulative UV load
• Train every worker — including seasonal and temporary staff — on the hazard before they begin celery work, not after the first case appears
• Record and investigate any case of skin blistering or inflammation among agricultural workers as a potential occupational injury, and review controls accordingly

One of the most common employer failures is issuing PPE in theory but not enforcing or monitoring its use in practice. Workers often remove protective sleeves in hot weather for comfort. The employer's responsibility does not end at providing equipment — it extends to ensuring that the work environment and culture make wearing it realistic and consistent.

Practical Controls That Work — and Ones That Do Not

The most effective control is physical exclusion: keeping plant sap off the skin entirely. This means full-length sleeves made from tightly woven, fluid-resistant fabric — not thin cotton, which saturates quickly and holds sap against the skin for extended periods. Nitrile or rubber gauntlet-style gloves that extend up the forearm are strongly preferable to short-cuffed gloves that leave a gap at the wrist, exactly where sap collects when workers reach into dense crop rows.

The second most effective control is washing. If sap contacts the skin, washing with soap and water within 30 minutes and before moving into sunlight can substantially reduce the severity of the reaction. Workers need to understand that this window exists and that washing promptly is a genuine intervention, not just hygiene.

Sunscreen applied over areas of sap contact can reduce UV penetration and limit the reaction if washing is not immediately available, but it is a weak control used alone. If sap has already absorbed into the skin layers, sunscreen limits but does not eliminate the photochemical reaction. It should not be treated as a substitute for PPE or washing.

Task scheduling — moving cutting, trimming, and washing operations to early morning or late afternoon when UV intensity is lower — is a useful supplementary measure but an unreliable primary one, since cloud cover and UV reflection vary and UV exposure can still be significant outside peak hours.

What a Worker Should Do If They Have Already Developed Blisters

A worker who develops blisters on the forearms after celery handling should report the reaction to their supervisor immediately and seek medical assessment. The blisters should not be deliberately burst, as broken skin creates an infection risk. Cool, damp compresses can relieve the burning sensation in the short term. The affected area should be kept out of sunlight while healing — continued UV exposure prolongs and worsens the reaction.

A medical or occupational health assessment should confirm the diagnosis and rule out secondary infection, which can develop if large blisters break and the underlying skin is not managed carefully. The worker should also be asked whether colleagues doing similar tasks have reported similar symptoms — phytophotodermatitis in one worker on a celery farm almost always means that others are at risk, and a group assessment of the work practice is warranted.

Workers should not return to unprotected celery handling until adequate controls are in place. Returning to the same task without PPE will trigger another episode, often more severe than the first.

What People Most Commonly Get Wrong About This Condition

The most persistent misconception is that the blisters are simply sunburn or heat rash, particularly because they appear after outdoor work. Sunburn does not produce the characteristic streaky blister pattern, and it does not produce the long-lasting brown hyperpigmentation that follows phytophotodermatitis. If a worker or supervisor dismisses the reaction as sunburn, the underlying cause goes unaddressed and further cases follow.

A second misunderstanding is that the reaction means the worker is allergic to celery and must be reassigned permanently. Phytophotodermatitis is not an allergy — it is a phototoxic reaction that will happen to almost anyone under the same conditions. The correct response is not to move the worker out of celery fields indefinitely, but to ensure that adequate protective measures are in place so that all workers can handle the crop safely.

Finally, many farm operators underestimate the severity of the occupational risk because individual cases are often dismissed as minor skin problems. Severe phytophotodermatitis can cause significant pain, temporary disability, secondary infection, and lasting skin discolouration. It is a recordable occupational skin injury, and repeated cases on the same farm indicate a systemic failure in hazard management that requires formal intervention — not individual treatment of each case in isolation.

Health at Work provides occupational health assessments for agricultural employers and farm workers, including skin hazard evaluations, worker health surveillance, and management of dermatological conditions arising from work with phototoxic crops.