Extension Toxicology Network

Toxicology Information Briefs

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised 9/93.



During mixing, loading and application of pesticides, the skin is the most likely body surface to come into contact with the product. Many pesticides can be absorbed through the skin into the blood, and can cause toxic effects. The amount of pesticide absorbed through the skin (percutaneous absorption) may be enough to produce severe toxic reactions including death. In addition, pesticides can also injure the skin directly, a process known as cutaneous toxicity. Skin irritation and skin rashes produced by irritating chemical substances are a very noticeable type of chemical toxicity. Skin infections by fungi (ringworm, athlete's foot, etc.), bacteria, or parasites are also very common medical problems and often have the same symptoms as skin irritation caused by chemical exposure. We live in a world filled with substances which can be irritating to our skin, and we use many of these irritating substances every day without great concern, because we have learned how to restrict our exposure.

The skin and the mucous membranes which cover the openings of our bodies to the external environment (such as in the nose and mouth), form protective barriers which keep water inside the body, and keep the outside (filled with bacteria, fungi, dust, dirt, etc.) from coming in. The skin is really an organ of the body, and a large one at that. The skin is much more than just a simple covering, it is multi-layered, and underneath the surface (which is composed of dead cells), are other layers composed of living cells which react to irritants when they get through. When an irritant reaches these sensitive live skin cells, they can only respond in a limited number of ways, the first of which is a general response to any irritating chemical or physical agent (like sunlight); inflammation. Inflammation has four components; redness, pain, heat and swelling. The degree of inflammation is a direct result of the degree of chemical or physical irritation (dose-response). If the damage is great enough to cause cell death, then the response will be much more severe, and can result in areas of the skin becoming "denuded" (loss of the layers, with the deeper layers being exposed to the surface). Because the response of the skin to many different physical and chemical irritants is similar, the causes of skin irritation must usually be diagnosed by a physician who specializes in skin problems (a dermatologist).

This Toxicology Information Brief (TIB) describes one of the most common toxic affects produced by pesticides and other chemicals, cutaneous toxicity in its many forms. Cutaneous toxic reactions account for approximately 1/3 of all pesticide related occupational problems, however pesticides are not the only chemicals which can cause skin toxicity. For example, allergic dermatitis produced by poison oak is the most frequent cause of temporary disability in forestry workers. Dermatitis means literally "inflammation of the skin." Most often dermatitis is referred to as a skin "rash," however, this term is very non-specific. There are many different types of "rashes" and they differ quite a bit in the way they appear and in how they are produced.

Some of the more frequently encountered dermatitis problems in humans and food animals are primary irritant dermatitis and allergic contact dermatitis.


This type of dermatitis is caused by chemical substances that directly irritate the skin (like caustic acids or bases). The symptoms may be similar to a slight burn (redness, itching, pain) or as severe as blisters, with peeling and open wounds (ulcerations). The areas of direct contact are usually the most affected and this is one of the ways it is recognized. Treatment consists of removal of the irritant by washing and prevention of further contact with the chemical. Steroid creams (such as 0.5% hydrocortisone preparations, available without prescription) may help alleviate pain and itching. When exposure to the irritant is prevented the irritation cannot occur. Thus, the use of appropriate protective equipment can completely prevent the development of primary irritant dermatitis.

Table 1. The following plants and pesticides may cause primary irritant dermatitis.

Sulfur Omite Methomyl Maneb Weed Oil
Captafol Folpet Kelthane Dinitro Benomyl Dacthal
Endosulfan Lindane Zineb Captan Chlorothalonil
Toxaphene Ziram Dinoseb TOK Organophosphates
Chloropicin Thiram Triazine Glyphosate  
Plants Flowers Trees        
Tomatoes Dieffenbachia Carrot Castor Bean Fig tree Sap
Mushroom Rubber Tree Daffodil Cucumber Buttercup
Parsnip Foxglove Turnip Tulip bulb Narcissus bulb
Parsley Cowslip Celery Milkweed  


The best example of allergic contact dermatitis (ACD) is poison oak and poison ivy dermatitis. This cutaneous toxic reaction is a true allergic response because the skin must be sensitized by exposure to the chemical (once or many times) and the result is a localized allergic reaction. Not everyone will develop ACD after exposure, and some workers may handle a potentially allergenic substance for years before ACD develops, or it may develop after a single exposure. The symptoms of ACD are exactly those of poison ivy or poison oak dermatitis, and vary from redness, itching and small blisters to widespread blisters that overlap forming very large fluid filled blisters. Treatment involves thorough washing to remove the allergen (in the case of poison ivy and oak it is the oils in the plants) followed by treatment to reduce the itching, pain and swelling. A topical corticosteroid cream may be very effective in reducing the symptoms. When large blisters break or are opened, care should be taken to prevent secondary infection of these raw areas. Local anesthetic creams (containing benzocaine) should be avoided since they also can act as contact sensitizers (may also cause allergic dermatitis) and may also delay healing.

Table 2. These plants and pesticides may cause allergic contact dermatitis (ACD).

Captan Captafol Benomyl Dichlorovos PCNB Zineb Maneb Formaldehyde
Naled Thiram Triazine Parathion Malathion TOK Cresol Some natural pyrethroides
Plants Flowers Trees              
Poison Ivy Primrose Cedar Poison Sumac Cashew Chrysanthemum Onions Garlic
Poison Oak English Ivy Pine Tulip bulbs Liverwort Narcissus Bulbs Lichens Celery


There are two basic types of photosensitization dermatitis. The first, which is most common in non-humans, is called phototoxic photosensitization dermatitis. Phototoxicity is not very common in humans whereas in domestic food animals it is the most common cutaneous toxic response. Phototoxic photosensivity occurs when a compound (a photosensitizer) is present in the body making the organism sensitive to sunlight. The condition of phototoxicity occurs only after exposure to sunlight. Signs of phototoxicity are sunburn-like reactions especially in non-pigmented areas. Some of the conditions and plants which cause phototoxic photosensitization in non-humans are listed in table 3.

Table 3. Plants and conditions that may cause photosensitization when ingested.

Tetradymia sp (Horsebrushes) Lecheguilla Lantana Kochia Tribulus terrestris (Goatshead) Hypericium sp. (St Johnswort)
Conditions / Other drugs          
Phenothiazines Sulfonamides Tetracyclines Copper Toxicosis in Sheep Blue-green algae poisoning Any condition that seriously damages the liver (pyrrolizidine alkaloid poisoning).

Contact phototoxic photosensitization is the most common occupational phototoxic reaction in humans, and is caused primarily by plants. This type of toxic reaction occurs when the photoactive chemical produced by the plant (or fungus) contacts the skin, is absorbed into the skin, and then activated by sunlight. The result is the same as sunburn, and varies in intensity dependent on the amount of chemical exposure, and the amount of exposure to sunlight. Plants which cause it are listed in table 4.

Table 4. Plants which cause contact photo-sensitization.

Figs Parsley Carrots
Dill Lime Buttercup
Mustard Klamath weed Celery (with pink rot)

The symptoms are redness, pain, blistering and, following recovery, hyperpigmentation of the affected area. Historians record that the ancient Egyptians knew of this reaction and used it to darken light areas of the skin. Some forms of toxic chemicals from plants are still used today to treat hypopigmentation (abnormally light pigmentation of the skin).

The second type of photosensitization dermatitis is the photoallergic reaction. This disorder is very similar in appearance to allergic contact dermatitis; however, sunlight is required to initiate the process. It requires prior exposure to the chemical and sunlight, and is not very common.


Chemicals can be absorbed through skin and into the blood stream causing toxic effects. The chemicals may also cause reactions on the skin surface. Some individuals may be particularly sensitive to a compound or a plant and others may experience little or no effects from contact. Determining the cause of dermatitis may be easy or it may be difficult. If I knew I walked through poison ivy and I develop a reaction, the connection is fairly obvious. However, if I have worked in the garden, or the exterminator visited a week ago and I have developed a rash the connections are not as obvious.

Finding out just what has caused the dermatitis may involve "patch testing" in which the patient's skin is exposed to small patches containing dilute solutions of the suspect agents. In this way, the offending chemical can be identified and measures taken to prevent or minimize future exposure. The best way to prevent cutaneous toxicity is the appropriate and correct use of protective clothing, and the use of safe handling and application procedures.

DISCLAIMER: The information in this brief does not in any way replace or supersede the information on the pesticide product label/ing or other regulatory requirements. Please refer to the pesticide product label/ing.