Giant Hogweed and Dogs: Identification, Exposure and What to Do

Updated July 2026

Giant hogweed is an invasive plant that can cause serious injury to people and pets.

The sap contains chemicals called furanocoumarins. These make exposed skin extremely sensitive to ultraviolet light. Contact may cause inflammation, burns, and blistering when the affected area is exposed to sunlight.

A dog’s coat provides some protection, but areas with thin or little hair can remain vulnerable. These include the muzzle, ears, belly and skin around the eyes.

Sap may also become trapped on the coat and later reach the dog’s skin, mouth or eyes when they lick or rub themselves.

Do not touch or cut a suspected giant hogweed plant to confirm its identity.

Move your dog away, prevent contact and report the location to the appropriate landowner or local authority.

For wider seasonal hazards, read Seasonal Pet Safety in Finchley.

The quick answer

When you see suspected giant hogweed:

• keep your dog on a lead
• move away without touching the plant
• do not allow sniffing, chewing or rubbing against it
• avoid breaking stems or leaves
• take a photograph from a safe distance
• record the exact location
• report plants found on public land
• do not attempt to remove the plant yourself

When your dog may have contacted the sap:

1. Move them into the shade and keep affected areas out of direct sunlight.
2. Wear gloves before touching contaminated fur or equipment.
3. Prevent licking and rubbing.
4. Contact your veterinary practice promptly.
5. Follow the veterinary team’s instructions about rinsing and further care.
6. Treat suspected eye exposure as urgent.

Do not wait for obvious blistering before seeking advice.

What is giant hogweed?

Giant hogweed is a large, invasive member of the carrot family.

The botanical name most commonly used in Britain is:

Heracleum mantegazzianum

The Royal Horticultural Society notes that Britain has four closely related naturalised giant-hogweed species. They look similar, and the name Heracleum mantegazzianum is commonly used to refer to them collectively. (RHS)

Giant hogweed was introduced to Britain as an ornamental plant during the nineteenth century and later escaped into the wild.

It is now found across the British Isles, particularly around:

• riverbanks
• canals
• streams
• railway land
• roadside verges
• rough ground
• woodland edges
• neglected gardens
• parks and open spaces

The plant can spread quickly and crowd out native vegetation. It is subject to restrictions due to its invasive nature and the danger posed by its sap. (GOV.UK)

What does giant hogweed look like?

A mature giant hogweed plant can be extremely large.

Possible identifying features include:

• a height of up to approximately five metres
• very large, deeply divided leaves
• leaves that may reach around 1.5 metres across
• thick, hollow stems
• coarse bristles
• green stems with purple or reddish blotches
• large umbrella-shaped clusters of white flowers
• a broad, spreading appearance

The stems are one of the most useful warning signs. They are thick and bristly, with distinctive purple or reddish blotching.

However, young or stunted plants may be much smaller.

Do not identify a plant solely by its height.

Giant hogweed flowers

The flowers usually appear in large white clusters known as umbels.

Each flower head may contain many smaller sections, creating an umbrella-like shape.

Similar flower arrangements are found on several related plants, including:

• common hogweed
• cow parsley
• wild carrot
• hemlock
• ground elder

The flower shape alone is therefore not enough to confirm giant hogweed.

Look at the plant’s overall size, leaves and stem from a safe distance.

Do not bend, cut or handle the plant to obtain a closer view.

Giant hogweed compared with common hogweed

Common hogweed is widespread in Britain and is generally much smaller.

Typical differences include:

Giant hogweed

• may reach up to five metres
• has extremely large, sharply divided leaves
• has thick, bristly stems
• often has clear purple blotches
• produces very large flower heads

Common hogweed

• normally grows to around two metres or less
• has smaller, more rounded leaves
• lacks the same prominent purple stem blotching
• has smaller flower heads
• appears less massive overall

The RHS warns that smaller giant-hogweed plants can still be confused with common hogweed. (RHS)

When you are unsure, keep your dog away and report the plant rather than approaching it.

Giant hogweed compared with cow parsley

Cow parsley is generally:

• much more delicate
• shorter
• thinner stemmed
• covered in softer, fern-like leaves
• likely to flower earlier in the year

Giant hogweed has much larger, coarser leaves and considerably thicker stems.

Photographs can help with identification, but do not rely on an image application or a social media comment when safety is involved.

A local authority, land manager or knowledgeable plant professional may need to confirm the species.

Why is giant hogweed dangerous?

Giant hogweed sap contains furanocoumarins.

These chemicals interfere with the skin’s ability to protect itself from ultraviolet light.

The resulting condition is called phytophotodermatitis.

In people, contact followed by sunlight can cause:

• burning
• severe redness
• blistering
• changes in skin colour
• long-lasting sensitivity
• scarring

The same phototoxic mechanism presents a risk to pets, particularly where the coat offers little protection. (RHS)

The sap becomes especially accessible when the plant is:

• cut
• crushed
• snapped
• chewed
• strimmed
• pulled up
• damaged by machinery

Brushing against damaged stems or bristly plant material may also expose skin and fur.

Which parts of a dog are most vulnerable?

A thick coat may reduce direct contact, but it does not make a dog completely safe.

More vulnerable areas can include:

• nose
• lips
• muzzle
• eyelids
• eyes
• ears
• belly
• groin
• armpits
• paw pads
• skin between the toes
• areas with clipped or thinning hair
• existing wounds

Short-coated, hairless or recently clipped dogs may have more exposed skin.

Sap on the outer coat can also be transferred when the dog:

• licks themselves
• scratches
• rubs their face
• rolls on bedding
• brushes against a person
• is towelled without precautions

PDSA warns that thinly haired areas may be affected and that sap reaching the eyes or being licked from the coat can cause further injury.

Does the dog need to eat giant hogweed?

No.

The main recognised hazards are contact with the plant’s sap and exposure to sunlight.

A dog may be exposed by:

• walking through damaged plants
• rubbing against stems
• investigating cut vegetation
• chewing a stem or leaf
• rolling near a recently strimmed patch
• stepping in sap
• licking contaminated fur

Chewing still needs to be taken seriously because it may expose the mouth, muzzle, tongue and surrounding skin.

Contact your vet whenever your dog has chewed on a suspected plant or has sap around their mouth.

Are the seeds the most dangerous part?

The old article stated that the seeds were particularly dangerous to dogs.

That emphasis has been removed.

The main practical risk is the phototoxic sap found within the plant, particularly when stems and leaves are damaged.

Seeds matter primarily because they allow the invasive plant to spread.

Do not collect, transport or dispose of giant-hogweed seeds or cuttings with ordinary garden waste.

Signs of giant-hogweed exposure in dogs

Possible signs may include:

• red or inflamed skin
• sensitivity when touched
• persistent licking
• rubbing the face
• pawing at the eyes or mouth
• swelling
• blistering
• moist or damaged skin
• reluctance to walk
• squinting
• excessive blinking
• discharge from an eye
• drooling after mouth exposure
• unusual distress

The severity may depend on:

• how much sap contacted the dog
• which body area was exposed
• whether sunlight reached the area
• how long the sap remained present
• whether the dog licked or rubbed it
• the amount of hair covering the skin

Do not assume the dog is safe simply because the skin appears normal immediately after the incident.

What should you do after possible contact?

Move the dog away

Do not allow further investigation.

Move into shade or indoors without walking through more of the plant.

Keep the dog on a lead so they cannot return to the area.

Protect the dog from sunlight

Keep the potentially exposed areas away from direct sunlight.

Move the dog into:

• a shaded building
• a vehicle only when it is cool and supervised
• an indoor space
• deep shade while arranging help

The phototoxic reaction is linked to ultraviolet exposure, so protecting the skin from sunlight is important. (RHS)

Protect yourself

Wear gloves before touching:

• the dog’s coat
• collar
• harness
• lead
• towels
• anything that may carry sap

Avoid touching your face or eyes.

Wash your hands and any exposed skin thoroughly afterwards.

Sap remaining on clothing, tools or equipment may still cause injury.

Prevent licking

Do not allow your dog to lick:

• their coat
• paws
• legs
• contaminated equipment

Use calm supervision while contacting your vet.

Do not improvise a tight bandage or place unsafe equipment around the dog’s neck.

Your veterinary team can advise how to reduce licking safely.

Contact your vet

Tell the veterinary practice:

• that giant-hogweed exposure is suspected
• when it happened
• which body parts may be affected
• whether the plant was damaged
• whether the dog licked it
• whether the eyes or mouth may be involved
• whether the dog has any current symptoms

Follow their instructions about rinsing, examination and transport.

Do not apply creams, oils or human medication.

Should you rinse your dog?

Promptly removing contamination may be important, but the safest method depends on where the sap is located and whether the eyes or mouth are involved.

Contact your veterinary practice immediately and follow their instructions.

When advised to rinse:

• wear gloves
• use plenty of clean water
• avoid spreading contamination to unaffected areas
• avoid scrubbing damaged skin
• prevent runoff reaching your own skin or eyes
• keep the dog out of sunlight afterwards

Do not use:

• bleach
• disinfectant
• alcohol
• essential oils
• stain remover
• household soap
• human burn cream
• an unprescribed medicated shampoo

Animal PoisonLine advises removing excess material from contaminated skin or fur and obtaining specialist advice rather than attempting unapproved home treatments.

Eye exposure is urgent

Sap reaching the eyes can cause serious damage.

Possible signs include:

• squinting
• keeping an eye closed
• pawing at the face
• redness
• watering
• discharge
• visible discomfort

Contact your vet immediately.

Tell them that exposure to phototoxic giant hogweed sap is suspected, and follow their emergency rinsing and transport instructions.

Do not:

• apply eye drops intended for people
• use leftover medication
• force the eyelids open roughly
• wait to see whether the eye improves

PDSA specifically warns that giant-hogweed sap entering an animal’s eyes can cause additional damage.

Do not make your dog vomit

Do not attempt to make your dog vomit after chewing a plant.

Never give:

• salt water
• hydrogen peroxide
• washing soda
• mustard
• human medication

These actions can cause further harm.

Contact your vet or Animal PoisonLine and follow professional advice. Animal PoisonLine is operated by the Veterinary Poisons Information Service and provides 24-hour specialist guidance for owners concerned about harmful exposure.

Should you bring a plant sample to the vet?

Do not handle or cut giant hogweed to collect a sample.

Instead:

• take photographs from a safe distance
• record the exact location
• photograph the leaves, stem and flowers where possible
• tell your vet why giant hogweed is suspected

Only provide plant material when your veterinary practice specifically requests it and you can do so without exposing yourself or spreading an invasive plant.

A photograph will often be safer than carrying contaminated vegetation.

How might a vet treat exposure?

Treatment will depend on:

• the body area involved
• whether the eyes or mouth were exposed
• the amount of skin affected
• whether blistering or inflammation has developed
• whether the dog has licked the sap
• the dog’s overall health

Your vet may need to examine the skin or eyes and decide how to clean, protect and monitor the affected area.

Do not predict or request specific treatments based on an online article.

The old page’s references to activated charcoal, stomach washing and guaranteed recovery have been removed because treatment must be based on the individual exposure and veterinary assessment.

When is emergency veterinary care needed?

Seek urgent veterinary advice when:

• sap may have reached an eye
• the dog chewed the plant
• the muzzle or mouth is affected
• blistering develops
• a large skin area was exposed
• the dog is in obvious pain
• swelling is increasing
• the dog cannot stop licking or rubbing
• the skin is becoming raw
• the dog appears generally unwell
• you are uncertain how much contact occurred

Do not wait for severe symptoms when eye or mouth exposure is possible.

What not to do

After suspected exposure, do not:

• leave your dog in direct sunlight
• touch contaminated fur with bare hands
• allow licking
• scrub the skin
• apply essential oils
• apply human burn cream
• give human painkillers
• force vomiting
• cut down the plant
• strim around it
• carry it home for identification
• place cuttings in ordinary garden waste
• post an exact location and encourage others to investigate it closely

Protect the dog, protect yourself and report the plant.

Preventing exposure on walks

When walking in an area where giant hogweed may grow:

• stay on clear paths
• keep your dog close near large unknown plants
• prevent chewing vegetation
• avoid piles of freshly cut stems
• keep away from cordoned areas
• follow signs from the council or landowner
• choose another route when uncertain
• warn other walkers without encouraging them to touch it

A long line should be shortened near unknown vegetation.

Do not allow the dog to disappear into dense growth beside a river or path.

Recently cut vegetation may still be hazardous

Do not assume a cut or wilted plant is safe.

Damaged stems and leaves may release sap, and contaminated tools or cuttings can remain hazardous.

Avoid:

• council cuttings
• strimmed verges containing unidentified stems
• piles of vegetation
• discarded garden waste
• broken plants beside paths

Keep your dog away and, where appropriate, report suspicious cut material.

Giant hogweed in gardens

When suspected giant hogweed is growing on private land:

• keep children and pets away
• do not mow or strim it
• do not cut flower heads
• do not dig it up without specialist guidance
• prevent contractors working nearby until warned
• obtain professional advice
• stop it being spread beyond the property

Government guidance also places responsibilities on landowners to prevent invasive plants from spreading and sets controls around treatment and disposal.

Do not put giant hogweed in ordinary garden waste

Invasive plant material may need specialist handling and disposal.

Do not:

• place it in household compost
• put cuttings into green waste without checking
• dump it elsewhere
• transport seeds or roots
• allow contaminated soil to spread

Contact the local authority or an appropriately qualified invasive-plant contractor for advice.

Government guidance warns that contaminated soil and plant material can cause further environmental damage and may be controlled waste.

Reporting giant hogweed in Barnet

When you see suspected giant hogweed on Barnet Council land:

1. Do not touch it.
2. Keep dogs and children away.
3. Take a photograph from a safe distance.
4. Record the precise location.
5. Use Barnet Council’s environmental or weed-reporting service.

Barnet Council states that it controls invasive species such as giant hogweed on council-owned land through targeted, repeated treatment. Plants on private land remain the responsibility of the landowner or managing agent.

For plants elsewhere, contact the organisation responsible for the land, which may be:

• another local authority
• Transport for London
• Network Rail
• a housing association
• a park trust
• a private landowner
• a waterway authority

Do not trespass to photograph or identify a plant.

Is it illegal to have giant hogweed?

Finding giant hogweed on land does not automatically mean the owner has committed an offence.

However, restrictions apply to invasive non-native plants, including controls on planting, growing, transporting, selling and allowing them to spread.

Giant hogweed should not be planted or deliberately caused to grow in the wild. (GOV.UK)

Landowners should obtain current professional advice about management and disposal rather than attempting casual removal.

Can dogs become affected without visible skin?

Yes.

A dog may have:

• sap beneath the coat
• contamination around the paws
• exposure inside the mouth
• sap near an eye
• irritation that is not yet obvious

Do not rely solely on visible blistering.

Contact your vet when meaningful contact is known or suspected.

Can giant hogweed cause blindness?

Eye exposure can cause serious damage and should be treated as an urgent matter.

However, the old article’s broad claim that exposure would cause permanent blindness has been removed.

The outcome depends on:

• whether sap entered the eye
• the amount involved
• how quickly help was obtained
• the extent of injury
• veterinary findings

Do not make predictions at home.

Contact your vet immediately and follow their instructions.

Can giant hogweed affect people?

Yes.

Human skin exposed to the sap and then sunlight may develop serious burns, blisters and long-lasting sensitivity.

When you contact the plant:

• move away
• cover the affected area from sunlight
• wash it thoroughly
• seek medical advice

NHS 111 can advise about non-life-threatening human exposure. Call 999 for a severe medical emergency.

The RHS recommends immediate washing, protection from sunlight and medical advice after skin contact. (RHS)

What if the dog rubs against you?

Sap on the dog’s coat can potentially transfer onto your skin.

Avoid unprotected contact.

Wear gloves and protect your arms while following veterinary instructions.

Do not:

• cuddle the dog against bare skin
• wipe the coat with an uncovered hand
• place contaminated clothing with ordinary laundry before checking it
• touch your face or eyes
• allow children to handle the dog

Wash exposed skin promptly and seek medical advice where needed.

Is every large white-flowered plant giant hogweed?

No.

Several UK plants produce white umbrella-shaped flowers.

These include:

• common hogweed
• cow parsley
• wild carrot
• hemlock
• ground elder
• angelica

Some of these plants can present hazards of their own.

Avoid touching or allowing your dog to eat an unknown plant simply because it does not appear large enough to be giant hogweed.

Use photographs and professional identification rather than handling it.

Giant hogweed and nervous dogs

A frightened or reactive dog may move suddenly when you try to inspect their face, paws or belly.

Do not force a painful dog onto their side or restrain them roughly.

Instead:

• move into shade
• prevent further licking
• keep handling to what is necessary
• call the vet
• explain that handling may be difficult
• follow their transport instructions

Pain can change behaviour.

A dog who normally accepts handling may growl or snap when an exposed area hurts.

My Rescue Dog Support in Finchley focuses on calm, low-pressure handling and creating space from avoidable hazards.

How I manage unknown plants during dog walks

I do not encourage dogs to push through dense or unknown vegetation.

When I notice a potentially hazardous plant, damaged vegetation or a cordoned area, I may:

• shorten the lead
• change direction
• cross the path
• use another route
• prevent sniffing or chewing
• record the location
• notify the owner
• report a suspected invasive plant

My walks are one-to-one and begin from the client’s home, so I can change the route around the individual dog rather than leading a group through the same vegetation.

Read about Solo Dog Walks in Finchley and Muswell Hill.

Frequently asked questions

Is giant hogweed poisonous to dogs?

It is hazardous to dogs.

The main danger is contact with phototoxic sap, which makes exposed skin more sensitive to sunlight. Sap entering the eyes or being licked from the coat may cause further injury. (PDSA)

What is the correct botanical name?

The name generally used for giant hogweed in Britain is Heracleum mantegazzianum.

The older article incorrectly used Heracleum maximum. The RHS notes that Britain has several closely related naturalised giant-hogweed species.

What does giant hogweed look like?

It is a very large plant with deeply divided leaves, thick, bristly stems, purple blotches, and large, white, umbrella-shaped flower heads.

Young plants may be much smaller.

Can a dog be hurt by brushing against it?

Yes, particularly when sap reaches thinly haired skin or damaged plant material is present.

Keep your dog away from all suspected giant hogweed.

What should I do when my dog touches it?

Move the dog into shade, prevent licking, wear gloves and contact your veterinary practice promptly.

Follow the vet’s advice about rinsing and examination.

Should I rinse the dog immediately?

Contact your vet and follow their instructions.

When rinsing is advised, use plenty of clean water while wearing gloves, avoid spreading contamination and keep the dog away from sunlight.

What if sap enters the dog’s eye?

Treat it as urgent.

Contact your vet immediately and follow their rinsing and transport instructions. Do not apply human eye medication.

Should I make my dog vomit after chewing it?

No.

Never attempt to make a dog vomit unless a veterinary professional specifically instructs you to do so.

Can I remove giant hogweed from a park?

No.

Do not touch, cut or remove it. Record the location and report it to the organisation responsible for the land.

Can I remove it from my own garden?

Professional removal is the safest option.

The plant is invasive, its sap is hazardous and disposal is controlled. Seek advice from a competent invasive-plant specialist. (RHS)

Should I bring a piece to the vet?

Do not cut or handle it.

Take photographs from a safe distance unless your vet specifically requests otherwise.

Is common hogweed safe?

Common hogweed is smaller and lacks the same prominent purple-blotched stem.

Avoid handling any unidentified hogweed, particularly when the plant is damaged.

Where should I report it in Finchley?

Report suspected plants on Barnet Council land through the council’s environmental or weed-reporting service. Include a photograph and precise location without touching the plant.

Keep your distance and report it

Giant hogweed should be treated with caution, but there is no reason to panic whenever you see a tall white-flowered plant.

Learn the main warning signs:

• exceptional size
• enormous divided leaves
• thick bristly stems
• purple blotches
• large white flower heads

Do not touch the plant to confirm its identity.

Move your dog away.

Keep suspected sap exposure out of sunlight.

Wear gloves.

Prevent licking.

Contact your vet promptly and report the plant to the responsible landowner.

For more outdoor hazard advice, read Dog Walking Safety Tips Every Owner Should Know.

Related Finchley Dog Walker guides

• Seasonal Pet Safety in Finchley
• Dog Walking Safety Tips
• Plants That Are Toxic to Dogs
• Walking Your Dog in the Countryside
• Summer Dog Safety Guide
• Dog First Aid Guide
• Is Your Dog in Need of Medical Care?
• Rescue Dog Support in Finchley
• Solo Dog Walks

Veterinary disclaimer

This article provides general information about giant hogweed and possible exposure in dogs.

It does not identify a plant, diagnose an injury, prescribe treatment or replace examination and advice from a veterinary surgeon.

Under the Veterinary Surgeons Act 1966, diagnosis and veterinary treatment are matters for an appropriately qualified veterinary surgeon.

Contact your veterinary practice promptly after suspected exposure to sap. Treat eye exposure, significant pain, blistering, swelling or mouth contact as urgent.