Overview

The concept called the "doctrine of signatures” (DOS) postulates that in some manner, plants which resemble the ailment or affected body part might be used to treat or lessen the symptoms of the illness. 

The DOS asserts that a plant's shape, colour, texture, and smell are among the physical attributes that indicate its therapeutic potential. This theory is an explanation of how certain cultures discovered medicinal uses of some plants. The DoS permeates all forms of folk medicine and is present in medical practices around the globe.¹ 

This article aims to present the key principles of the "doctrine of signatures and explain how this concept was applied historically. Furthermore, some modern interpretations of this phenomenon, which is also known as the “language of plants”, will be discussed.

Origins and historical development

Humans have been using nature's healing powers for a variety of illnesses for thousands of years. The doctrine of signatures was an essential and life-saving guide, especially throughout the sixteenth and seventeenth centuries when the powers of herbal medicine extended the spiritual and physical domains.

Paracelsus established the theoretical framework for the doctrine of signatures. He recognised a pharmacological association between the shape, colour, and texture of different plant materials and the human anatomy, adhering to the theory that "similar cured similar."² This concept was cited by the Greek writers and it was widely employed in herbal medicine during the Renaissance.² 

The main English proponent of the DOS, William Cole, thought that although some plants were marked with signatures "to set man on the right track," others were left unmarked to promote human discovery. Cole believed that St. John's wort (Hypericum perforatum, Clusiaceae) was used to heal skin conditions because of its skin-like glands. He also claimed that because walnuts "have the perfect signatures of the head," they are effective in treating conditions of the head.

Nowadays, in the age of evidence-based medicine, where treatment is only considered to be active if the molecular mechanism behind it has been uncovered and its effectiveness has been demonstrated in double-blind, placebo-controlled, and randomised research, traditional methods of healing such as the DOS, are becoming less and less common. 

Nevertheless, the DOS is living on, in extra-academic herbalism and alternative medicine. In fact, eighty per cent of the world's population still relies on traditional medicines as their primary source of healing.³

Key principles 

The idea that all living things are related to one another forms the foundation of the DOS. There are similarities between human beings and natural species in terms of form, colour, and scent, as well as humoral, pathological, and astrological characteristics.⁴ The DOS started with the premise that everything that God has made has a sign or signature. That sign provides an explanation to the item's creation's purpose.⁵ Hence, the DOS more closely resembles religious doctrine rather than scientific theory in many ways. 

The application of the DOS has certain restrictions. It doesn't provide a complete picture of a plant as the right dosage, method of herb preparation, and potential interactions (synergy or interference) between different herbal medicines are all unaddressed by this philosophy. Similar to this, the doctrine of signature is unable to fully explain the purpose of a remedy. The applicability is restricted since a cure acts more deeply and on several levels. Hence, the DOS does not apply to the effects of a remedy.

Examples in nature

Some examples in nature that are most frequently connected to the Doctrine of Signatures are listed below. Every plant is considered to symbolise a certain bodily component because it not only has a distinctive appearance but also contains nutrients that support the correct functioning of that organ.

Eyebright for the eyes

Herbs such as Eyebright (Euphrasia officinalis) have long been used medicinally to treat eye conditions. Eyebright may help irritated, inflamed eyes, according to preliminary research, but more thorough human studies are required. With their black centres, darker veins, and white petals, eyebright flowers can give the impression of being similar to the human eye.

Carrot for eyes

The majority of us were taught as children that eating carrots is beneficial to our eyes. Indeed, carrots are a great source of Vitamin A, which is necessary for maintaining healthy eyesight. The resemblance between the carrot and the eyeball when chopped widthwise is remarkable. A carrot's core has a black centre with a ring surrounding it when cut short. And if you examine it more closely, you may notice veins that resemble those in an eye.⁶ 

Ginger for stomach

Ginger soothes digestive discomfort and has a look similar to the intestines with its knobby protrusions. According to studies, ginger helps relieve gastrointestinal problems like nausea, vomiting, and indigestion.⁷

Tomato for heart

Similar to the human heart, the tomato has four chambers and is red. Beta-carotene, folate, potassium, and flavonoids found in tomatoes improve cardiovascular health by lowering blood pressure and LDL cholesterol. Tomatoes include lycopene, which helps lower the risk of stroke.⁸

Walnuts for brain

Walnuts resemble our brains in appearance and share characteristics such as having a hard shell covering a spongy, mushy interior. The walnut's lines and wrinkles bear a striking resemblance to the brain's neocortex. Remarkably, the exceptionally high concentration of omega-3, together with vitamin B9, vitamin E, and several antioxidants, aids in the development of neurotransmitters in the brain and enhances cognitive performance.

Kidney beans for kidneys 

Kidney beans, as the name suggests, look exactly like human kidneys. Many of the dietary elements that support kidney health can be found in kidney beans. These tiny red beans contain plenty of fibre, minerals, and vitamin B12. Kidney beans are a healthy choice for diabetics because they are low in fat and low on the glycemic index.

Citrus for breast

Sliced citrus fruits have a similar appearance to the breast's mammary glands, are packed with nutrients that are essential for breast health, and may even prevent breast cancer.⁹

Lungwort for lungs

Lungmoss, sometimes known as lungwort or lung lichen, is a plant used in herbal medicine which is believed to benefit the lungs. It was traditionally used to treat whooping cough and relieve chest colds due to the fact that its speckled leaves resemble lungs.

Grapes for the cardiovascular system

It's thought that grapes are beneficial to the cardiovascular system. Clusters of grapes look like the alveoli, which are tissue formations found inside the lungs. When suffering from a cold or cough associated with asthma, consuming grape juice can help clear the airways and enhance lung function. Additionally, a substance found in grape seeds called proanthocyanidin has heart-protective properties.¹⁰

Avocado for uterus

An avocado's oval form is comparable to that of the uterus. Furthermore, avocado contains a lot of potassium and folate, two minerals that are extremely beneficial for expectant mothers.¹¹ An interesting fact is that avocados take 9 months to grow from seed to ripened fruit.

Modern interpretations and critiques

The DOS hasn't received much critical scrutiny in spite of its long presence.³ Thus, this concept has caused numerous fatalities and serious diseases and is now regarded as pseudoscience. For example, birthwort (so-called because it resembles the uterus), which was historically frequently used to induce pregnancy, contains aristolochic acid, which is highly harmful to the kidneys and carcinogenic.²² An in-depth analysis of the DOS points to four conclusions: 

1. No proof exists that the identification of morphological plant signatures has ever resulted in the discovery of therapeutic benefits
2. Rather than being a priori indicators of the potential therapeutic value of plants, signatures are post hoc attributions
3. Redefining signatures to take into account organoleptic qualities linked to therapeutic benefit is beneficial. For instance, pharmacopoeias frequently include plants with strong scents or harsh tastes
4. DOS should be viewed as a means of information dissemination, which is what it is essentially

Furthermore, opponents of this medical practice contend that because of technological improvements in surgery, medicine, and illness diagnosis, we no longer need to rely on antiquated ideas.

FAQs

How might the doctrine of signatures help my condition?

Even though adhering strictly to the Doctrine of Signatures is not recommended, it can't harm to use visual cues to help you recall which fruits, vegetables, and herbs are good for particular sections of your body. For instance, since the core of a carrot resembles an eye, you might remember to eat an extra carrot as a snack when considering how to preserve your vision. 

Is the doctrine of signatures accurate?

The idea that the forms and colours of plants aid in the identification of their medicinal applications is unsupported by scientific research.³

Summary

According to the ancient concept known as the doctrine of signature, plant parts that resemble human or animal body parts have practical significance in the treatment of diseases connected to that body part. The contemporary interpretation of this theory asserts that every plant has a pattern that functions as a signal or sign and resembles a physiological function or body organ. There are differences in the recognition and acceptance of the signs found in nature and the world around us. Although the DOS is a useful tool, one shouldn't rely completely on it to determine whether a herb has medicinal qualities.