I’ve spent enough time in the garden to know one thing for sure: not every rash is poison ivy’s fault.

A few summers ago, I came inside after cutting herbs on a hot afternoon—parsley, dill, maybe some wild Queen Anne’s lace along the way—and woke up the next morning looking like I’d fallen asleep under a heat lamp. Red splotches covered my arms like a blotchy sunburn. Weird, I thought. But by the end of the week, those red marks had darkened into stubborn brown stains that clung to my skin for months.

That was the day I learned about phototoxic plants.

These are the sneaky ones. They don’t itch like poison ivy. They don’t sting like nettles. In fact, they look downright harmless—sometimes even beautiful. But hidden in their sap are natural chemicals that react with sunlight in a way your skin definitely won’t thank you for. Add UV rays to the mix, and voilà: welcome to the world of phytophotodermatitis (a.k.a. “plant + sun = mysterious rash”).

The wild part? This reaction isn’t based on allergies. It can happen to anyone, as long as the conditions are right: plant juice + skin + sunlight. That’s it.

Over the years, I’ve learned which plants to treat with a little more caution. Some are weeds along the roadside. Some are edible favorites growing in your kitchen garden right now. And every single one has the potential to leave its mark—literally—if you’re not careful.

Here are 12 phototoxic plants that can surprise even the most seasoned gardener.

What Does “Phototoxic” Even Mean?

Spend a few hours in the garden and come back with streaky red welts or blistered skin, and you might assume poison ivy got you. But if the pattern looks odd—like drips, splashes, or handprints—the real culprit could be something else entirely: a phototoxic plant.

The term phototoxic literally means “toxic in the presence of light.” Some plants produce natural compounds, most often furanocoumarins, that are harmless until they touch your skin and meet ultraviolet (UV) sunlight. Once sunlight activates them, they flip into high-energy molecules that damage skin cells. Dermatologists call the reaction phytophotodermatitis—plant-light dermatitis—or more casually, “meadow grass dermatitis.”

Unlike an allergy, which depends on your immune system’s sensitivity, phototoxicity is a straightforward chemical burn. Sap or juice lands on your skin, UV light triggers the chemistry, and within 24–48 hours you see redness, blistering, or dark patches that can linger long after the rash itself fades.

In other words, the garden didn’t just irritate your skin—it gave you a sun-powered chemical burn.

The Science Behind the Rash

On their own, most plant saps and juices seem harmless. The trouble starts when certain natural compounds—most famously furocoumarins—land on your skin and then meet sunlight. These compounds act like tiny chemical time bombs, quiet until the moment ultraviolet (UV-A and UV-B) rays strike.

Once activated by light, they generate reactive oxygen molecules—unstable particles that tear into nearby skin cells. DNA and proteins get damaged, the outer skin layer becomes inflamed, and the body responds much the way it does to a burn.

Other plants use different chemistry but trigger the same chain reaction. Hypericin in St. John’s wort and fagopyrin in buckwheat are two examples. In every case, the result is what dermatologists call phytophotodermatitis—literally, “plant + light + skin inflammation.”

Unlike an allergy, which depends on your immune system’s sensitivity, a phototoxic reaction is universal: if enough plant compound and sunlight come together, anyone’s skin can develop the telltale rash.

Symptoms of Phototoxic Plant Contact

One of the most surprising things about phototoxic reactions is that they don’t appear right away. You might brush against a plant while weeding in the morning, feel perfectly fine through the day, and then wake up the next morning with skin that looks and feels like it’s been burned.

When plant sap containing furocoumarins, hypericin, or fagopyrin interacts with sunlight, the skin damage unfolds gradually. Typical signs include:

• Redness that mimics a sunburn
• Itching or a burning sensation that worsens over time
• Noticeable swelling in the exposed area
• Blisters or streaks resembling a second-degree burn
• Peeling or flaking as the skin begins to heal
• Long-lasting dark patches (hyperpigmentation) that can linger for months

The rash usually takes 24 to 48 hours to fully appear, often getting worse before it improves. While most cases resolve in a week or two, the lingering dark stains are the telltale reminder of phytophotodermatitis.

How Dangerous Are Phototoxic Reactions

Most phototoxic plants are not poisonous by themselves. The risk appears when their natural compounds—mainly furocoumarins—contact human skin and are then activated by sunlight. As one dermatology review explains, furocoumarins are “photodynamically active substances that, once exposed to UV-A, generate reactive oxygen species and damage DNA in skin cells” (J Eur Acad Dermatol Venereol, 2017; PubMed).

The danger level depends heavily on the plant. Giant hogweed (Heracleum mantegazzianum) is among the most hazardous. Case studies show that its sap can cause blistering burns resembling second-degree injuries, with scarring and long-lasting hyperpigmentation (Br J Dermatol; ScienceDirect; JPRAS).

By comparison, common kitchen crops such as parsley, celery, and dill contain much lower concentrations of furocoumarins. The European Food Safety Authority has noted that normal handling or consumption carries “minimal risk under usual exposure,” though skin reactions are still possible when harvesting outdoors in bright sunlight.

Children are more vulnerable because of thinner skin, and people in outdoor professions—farmers, gardeners, landscapers, and florists—experience a higher rate of phototoxic dermatitis due to repeated exposure (MDPI, 2024; MDPI Review).

Most reactions heal within one to two weeks, though dark staining of the skin can persist for months. In rare cases, repeated or high-level exposures may even increase cancer risk, since psoralens and other furocoumarins show photocarcinogenic potential under chronic conditions (Food and Chemical Toxicology, 2019; ScienceDirect).

10 Common Phototoxic Plants That Can Burn Your Skin in Sunlight

1. Giant Hogweed (Heracleum mantegazzianum)

Giant hogweed is infamous for the severity of its reactions. Native to the Caucasus and introduced as an ornamental, it now invades riverbanks, roadsides, and neglected fields. Mature plants can tower up to 15 feet tall, with broad leaves and umbrella-like flower clusters that look deceptively attractive.

The real danger is in its sap, which is rich in furocoumarins such as psoralens. When this watery sap touches skin and is exposed to UV sunlight, it triggers severe phototoxic burns. Reactions may start as redness and blistering but can progress to painful wounds resembling second-degree burns. Even after healing, dark scars and pigmentation can last for months or years. Because of these risks, giant hogweed is officially listed as a noxious weed in many regions, and removing it safely requires protective clothing and extreme caution.

2. Fig Tree (Ficus carica)

If you’ve ever pruned a fig on a hot July afternoon, you may already know the sting. The tree’s milky sap feels harmless at first, but studies show it contains furocoumarins like psoralens that can trigger phytophotodermatitis once sunlight hits the skin.

Dermatology case reports document blistering and hyperpigmentation lasting for weeks—something I’ve seen firsthand when a friend ended up with dark streaks on her arms after cutting back a vigorous fig hedge without gloves.

The reaction is not rare among gardeners or food workers, and the medical literature confirms figs are one of the most common fruit-related causes of light-triggered dermatitis. The fix is simple: gloves, long sleeves, and a quick wash after pruning make fig season safe and sweet again.

3. St. John’s Wort (Hypericum perforatum)

St. John’s wort is one of those plants that looks cheerful in bloom—bright yellow flowers catching the sun—but it hides a complicated chemistry. The pigment hypericin is a known photosensitizer.

Clinical reviews show that it absorbs UV radiation and produces reactive oxygen species that injure skin cells. That’s why both handling the plant and even taking it internally as an herbal supplement can make your skin more sensitive to sunlight.

I’ve noticed fair-skinned gardeners react the fastest: redness, itching, and sometimes blistering after just a short time outdoors. Researchers warn the effect is dose-dependent—more exposure, bigger reaction. It’s a reminder that a plant valued for its healing properties also requires respect in the garden.

4. Anise (Pimpinella anisum)

Anise is grown as much for its licorice-scented seeds as for its lacy white umbels, but it shares the same family (Apiaceae) as parsley and parsnip—and with it, the potential for phototoxic sap.

The seeds themselves are safe to handle, but the green parts of the plant contain psoralens that can sensitize the skin.

Agricultural reports note occasional cases of dermatitis in workers handling fresh anise crops, especially in Mediterranean regions where sun exposure is high. I’ve brushed against it without gloves on a clear day and ended up with a faint rash that lasted longer than expected. The lesson: treat anise like its cousins—handle with care in the sun, and wash promptly after harvest.

5. Dill (Anethum graveolens)

Dill is beloved for flavoring pickles and attracting pollinators, but its feathery foliage also carries psoralens. Farm studies describe “dill pickers’ dermatitis,” a form of phytophotodermatitis seen in workers exposed to sap under UV light.

Symptoms are typically less severe than hogweed or parsnip, but they can still include redness, irritation, and post-inflammatory pigmentation. I’ve noticed that pruning or pulling large stands of dill without gloves on a sunny morning often leaves behind faint rash-like marks by evening. It’s a small risk compared to the joy of a good dill harvest, but it’s a reminder that even familiar kitchen herbs deserve a little respect.

6. Skimmia (Skimmia japonica)

Skimmia is a staple in shaded gardens, admired for its fragrant spring blossoms and clusters of red berries that brighten the winter landscape.

Yet this evergreen shrub is not entirely without risk. Its leaves and stems contain phototoxic compounds, and pruning without gloves on sunny days has been linked to mild cases of dermatitis. British horticultural bulletins regularly remind gardeners that sap exposure, combined with UV light, may result in redness, itching, or irritation.

While the reaction is far less dramatic than that caused by hogweed or parsnip, sensitive gardeners can still develop uncomfortable rashes or darkened patches that last several weeks.

Wearing gloves and washing exposed skin immediately after pruning is usually enough to prevent problems. Skimmia remains a safe and beautiful shrub—but one that benefits from a careful touch.

7. Buttercup (Ranunculus spp.)

Buttercups may look harmless carpeting lawns and meadows with shining yellow flowers, but their chemistry tells another story. These plants contain ranunculin, which converts into protoanemonin when the tissues are damaged.

Protoanemonin is a known irritant that can cause burn-like blisters, redness, and swelling when it contacts skin and sunlight intensifies the reaction.

Reports of buttercup dermatitis go back centuries, and field workers handling large stands have long recognized the risk. While symptoms are typically mild and short-lived, they can be painful and leave behind patches of temporary hyperpigmentation.

Children, who often handle buttercups for play, are especially vulnerable. Like many plants in the buttercup family, their beauty is best admired with caution—enjoy the flowers, but avoid direct sap-to-skin contact in bright conditions.

8. Parsnip (Pastinaca sativa)

Parsnips are prized in the kitchen for their sweet, nutty roots, but in the garden their leafy tops carry a hidden risk. The sap contains furocoumarins, chemical compounds that can cause skin to react violently with sunlight. Farmers have long described this as “parsnip picker’s rash,” and dermatology studies back it up: redness often appears within 24 hours, followed by blisters and brown discoloration that may linger for weeks.

Home gardeners aren’t handling fields of parsnip, so reactions are usually less severe, but the risk is still there—especially during weeding or thinning on hot, sunny days. Gloves and long sleeves are simple protection, and rinsing skin quickly if sap gets on you is often enough to prevent problems. The roots themselves are perfectly safe to eat, so the lesson here is not to avoid parsnips, just to handle the tops with a little more respect.

9. Wild Carrot (Daucus carota, Queen Anne’s Lace)

Wild carrot, better known as Queen Anne’s lace, is one of the most deceptive members of the carrot family. Its airy white umbels look like lace scattered across roadsides and meadows, but the sap tells another story.

Like parsnip and hogweed, it contains psoralens, which sensitize the skin to sunlight. Within a day of contact, gardeners often notice streaky rashes or drip-shaped burns, and the dark pigmentation that follows can last for months.

Because wild carrot is so widespread—and often mistaken for a harmless wildflower—it’s a frequent cause of mysterious rashes in summer.

Unlike poison ivy, which only affects those allergic to urushiol, wild carrot’s reaction is universal: if sap and sun meet your skin, anyone can react. That’s why hikers, children, and roadside workers often end up with marks they can’t quite explain.

10. Celery (Apium graveolens)

Celery is a surprising entry on the phototoxic list because it’s such a familiar kitchen staple. Yet occupational health studies consistently mention “celery picker’s rash,” particularly in workers harvesting under bright sun.

The stalks and foliage contain low levels of psoralens—not enough to make celery dangerous to eat, but sufficient to irritate skin when handling is combined with UV exposure.

For the home gardener, reactions are usually mild: a bit of redness, itching, or faint pigmentation after cutting stalks without protection.

Still, it’s worth remembering that celery belongs to the same family as parsnip and hogweed, and it shares some of their chemistry. Harvesting in the cool of the morning or evening, wearing gloves, and rinsing hands afterward make the task worry-free. Celery may be common, but it’s another reminder that even the most ordinary vegetables can come with a hidden sting.

11. Rue (Ruta graveolens)

Rue has an old-world charm, with its blue-green foliage and strong, resinous scent. But ask any gardener who’s cut it back under full sun, and they’ll tell you how quickly admiration can turn into regret. The plant’s oils contain high levels of bergapten and xanthotoxin, both powerful furocoumarins.

Dermatology texts describe the resulting reaction as “classic phytophotodermatitis”: red streaks, blisters, and pigmentation that can last months.

I once met a gardener who said she could trace the exact outline of her pruning shears on her forearm after a sunny-day encounter with rue sap. Unlike poison ivy, this isn’t an allergy—anyone can react if the conditions line up. Gloves and cloudy-weather pruning aren’t just smart; they’re essential if you plan to grow rue safely.

12. Parsley (Petroselinum crispum)

Parsley seems so innocent in the kitchen garden, but its sap contains furocoumarins, the same class of compounds found in hogweed and wild parsnip. The amounts are much lower, which is why most home cooks never notice a problem.

But harvest parsley in bright sun, rub your forearm across the foliage, and you may see the evidence a day later: red streaks, mild blistering, and lingering brown marks.

Researchers have documented “harvester’s dermatitis” in field workers cutting parsley in bulk, and while home gardeners face lower risk, the reaction is real. I’ve found that even a quick rinse after picking a handful makes the difference between a fresh bunch for the kitchen and a rash that overstays its welcome.

13: Lime (Citrus aurantiifolia)

Limes add zest to drinks and brighten countless recipes, but in the garden or kitchen they can deliver more than just flavor. The juice, peel oils, and even crushed leaves contain bergapten and other psoralens, compounds well known for their phototoxic effects. When lime juice lingers on the skin and sunlight follows, the result can be dramatic: red streaks, blistering burns, and brown stains that can take weeks or even months to fade.

This condition is so common it has a nickname—“margarita dermatitis.” Dermatologists frequently report cases in bartenders, cooks, and vacationers who squeeze limes outdoors. In tropical and coastal regions, it’s one of the leading causes of phytophotodermatitis, second only to hogweed and wild parsnip.

The reaction doesn’t strike right away; it often appears within 24 to 48 hours, making it easy to mistake for sunburn. Unlike an allergy, it can happen to anyone, given enough juice and enough sun. The solution is simple: rinse your hands and arms thoroughly after handling limes and avoid direct UV exposure until you’re sure no residue remains. The fruit itself is perfectly safe to eat—it’s just the skin that sometimes pays the price.