Cinnamaldehyde (CNAD) lowers inflammatory reactions, oxidative stress, and apoptosis of the liver in Salmonella typhimurium-infected mice. Supplementation of CNAD might be a good preventive method to alleviate the liver damage caused by Salmonella typhimurium infection in humans and animals [14]. Moreover, cinnamon bark essential oils (EOs) have been shown to cause oxidative stress to Klebsiella pneumoniae, resulting in the loss of cell viability [15]. Both oregano and cinnamon bark EOs have strong antibacterial properties. Aljaafari et al. [16] have shown that the antimicrobial properties of essential oils (EOs) are based on the mode of action in relation to membrane disruption, efflux inhibition, the increase in membrane permeability, and the decrease in intracellular ATP. These essential oil compounds can be used as potential agents against bacteria, fungi, and viruses. In the future, the integration of EOs uses can lead to many clinical applications.

In medicine, the essential oils in cinnamon behave like other volatile oils. It has also been used in the treatment of digestive system problems and colds. The essential oils in cinnamon also have antimicrobial properties and are used as a preservative in some foods. Cinnamon has been reported to have remarkable pharmacological effects in the treatment of diabetes type 2 resistant to both mellitus and insulin; however, the plant material used in the study was mainly from cassia and only some of the plant material was from C. zeylanicum. Cinnamon has traditionally been used for toothache and to fight bad breath, and its regular use is thought to cure the common cold and support digestion [17]. It is noted that regular drinking of C. zeylanicum tea made from the bark could be helpful in oxidative-stress-related illness in humans, since it has considerable antioxidant potential. Cinnamon may also act as an aphrodisiac. One teaspoon of cinnamon has as many antioxidants as a cup of pomegranate juice and half a cup of blueberries [17].

Nanocapsules with cinnamon-thyme-ginger composite essential oils prepared with chitosan as the wall via ionic gellification reaction were tested in medicine and revealed durable antibacterial activity against Escherichia coli, Bacillus subtilis, and Staphylococcus aureus. Composite essential oil nanocapsules CEO-NPs can be applied as a strong long-lasting natural preservative [18].

Scientific research has confirmed the effectiveness of cinnamon in fighting microbes, viruses, fungi, oxidants, tumours, and hypertension. It also has antidiabetic, gastro-protective, and immune modulatory potential [17]. However, the popular use of cinnamon has also resulted in several reports of side effects from its short- and long-term use. The most common negative effects were disorders of the stomach and bowels, as well as allergic reactions, which were self-controlling in most cases. Although cinnamon is safe as a spice and/or flavour, prolonged and enlarged use may be a health risk, and hence, in medicinal uses, it should be clinically monitored [19].

Cinnamon coats and dries the mouth and throat, leading to coughing, gagging, vomiting, and the inhalation of cinnamon, causing throat irritation, breathing difficulties, and a risk of pneumonia or lung collapse [20,21]. Cinnamon contact stomatitis (CCS) is also a sporadic reaction to the consumption of foods containing artificial cinnamon flavour. Physicians who treat patients with oral conditions ought to be aware of CCS to correctly diagnose and manage this condition [22]. Contact stomatitis, which is related to the use of cinnamon flavourings, is rather rare. The symptoms, as well as the histopathologic features of this disease are non-specific. They may be similar to other inflammatory illnesses of the oral mucosa, which causes problems in diagnosis. Patients develop white and erythematous spots of rapid occurrence, with an associated sensation of burning. High levels of coumarin and cinnamaldehyde might be associated with mouth sores [23]. High levels of coumarin and cinnamaldehyde might be also correlated to liver damage and low blood sugar [24]; such high levels may increase the risk of cancer, breathing problems, and interaction with certain medications [11].

Oral lesions caused by a reaction to cinnamon flavouring agents are rather uncommon and are probably unrecognized by many physicians. Most patients feel a “burning sensation”, which is the primary symptom. Clinically, lesions present as erythematous patches with different degrees of superimposed keratosis or ulceration. The lesions are usually limited to the buccal mucosa and lateral border of the tongue. The responsible agent was most frequently cinnamon-flavouring chewing gum, and symptoms usually eased within 1 to 2 days after the last use of the product containing cinnamon [25].

Cinnamon oils and extracts possess antifungal properties against serious plant diseases (Table 2). Wilson et al. [26] indicated that, out of 49 essential oils tested, cinnamon leaf C. zeylanicum showed the strongest antifungal activity against Botrytis cinerea. MontesBelmont and Carvajal [27] found that Aspergillus flavus was fully inhibited by C. zeylanicum. In other studies, C. zeylanicum proved to be fungicidal towards pathogens (Colletotrichum musae, Lasiodiplodia thebromae, and Fusarium proliferatum) isolated from bananas [28]. Cinnamon also had an antifungal effect against Oidium murrayae [29] and harnessed conidial germination of Colletotrichum gloesporioides [30]. In in vitro tests, it proved to have a significant mycelial inhibition in corn rot Fusarium oxysporum f. sp. gladioli [31] and to be very effective against the growth of Rhizoctonia solani [32]. Moreover, cinnamon has powerful antifungal activity towards early tomato blight (Alternaria solani) [33]. Botrytis cinerea is a serious problem, especially in horticultural crops. The investigations of Wang et al. [34] demonstrated that cinnamon microemulsions possessed high in vivo control properties against gray mould of pears, B. cinerea. The influence of C. zeylanicum organic powder on the growth of B. cinerea and its effect on tomato plants have also been assessed. Cinnamon bark powder and also its water suspensions and filtrates controlled B. cinerea; moreover, tomato plants sprayed with cinnamon developed better than the control plants [35].