Black Walnut Hull Side Effects

Black walnut has a long history of use in agriculture, traditional medicine, and commercial industry. Native Americans used the hulls to make dyes. Today, black walnut hull extracts are used in natural hair color formulas and self-tanning lotions.

The kernels of black walnuts (Juglans nigra) are not the only part of the plant that offers health benefits. While research is still emerging, according to one study in Plants, the shells themselves also have antioxidant, antibacterial, and antimicrobial properties. But before you add black walnut hull powders or tinctures to your regimen, be aware of these potential side effects.

Allergic Reactions

The U.S. Food and Drug Administration (FDA) categorizes black walnuts as a tree nut, which is a common food allergy. You should avoid black walnuts and their products — including hull extracts — if you have a known sensitivity to other tree nuts, according to Food Allergy Research & Education (FARE).

Allergic reactions to food range in severity. According to Mayo Clinic, the most common symptoms include a tingly or itchy mouth, swelling of the lips or other parts of the body, stomach pain, nausea, vomiting, wheezing, and lightheadedness.

A severe allergic reaction requires immediate medical attention. Symptoms of a life-threatening reaction include difficulty breathing, a swollen throat or the feeling of a lump in the throat making it hard to breathe, rapid pulse, dizziness or fainting, or a severe drop in blood pressure.

Toxic to People

The active compound in black walnut is juglone. While this substance is found in all parts of the tree, the fruit, roots, and hulls contain the highest concentrations, according to Pacific Northwest Handbooks (a joint publication from Oregon State University, Washington State University, and the University of Idaho).

Juglone is toxic to people and can create unpleasant side effects, according to Cleveland Clinic. Exposure to this chemical can cause pain, itching, and severe blistering. Hulling black walnuts can expose you to juglone, but woodworkers using black walnut wood or gardeners working near a tree can also get an irritating reaction. Juglone can also stain your hands a dark color that lasts a few weeks. Cleveland Clinic recommends wearing gloves when handling black walnuts.

Toxic to Animals

Juglone is poisonous to horses and dogs, according to Colorado State University. In horses, it can cause laminitis (a foot disease) or acute lameness. Black walnut hulls are sometimes found in wood shavings used in horse bedding material. Even bedding material with as little as 20 percent black walnut hulls present can result in laminitis.

Another hazard exists to dogs or other animals that eat nuts that have fallen to the ground. If the walnuts become moldy, they may contain a neurotoxin called penitrem A. Signs of poisoning often take a few hours after the moldy walnuts are eaten and can include convulsions, hyperthermia, rapid breathing, urination, and dilated pupils, according to Colorado State University.

Toxic to Plants

If you have black walnut trees on your property, be aware that juglone may affect other vegetation growing nearby, with the toxic reach of a mature tree extending as far as 80 feet away, according to the University of Wisconsin-Madison. Affected plants may have wilting or yellowing leaves and stunted growth, and they may die.

Black walnut toxicity can affect vegetables, flowers, trees, shrubs, vines, grasses, and field crops, University of Wisconsin-Madison notes. Food plants that are particularly vulnerable to juglone poisoning include asparagus, cabbage, eggplant, pepper, potato, rhubarb, and tomato. Plants that are more tolerant of living near black walnut trees include beans, beets, carrots, corn, melons, onions, parsnips, and squash.