POROPORO: Topical Support

Posted: September 2022
Author: Phil Rasmussen | M.Pharm., M.P.S., Dip. Herb. Med.; M.N.I.M.H.(UK), F.N.Z.A.M.H.

Poroporo is the name given to two closely related species of a plant native to Aotearoa, Solanum aviculare and Solanum laciniatum. As with Akeake (Dodonaea viscosa), it's not just here that this plant grows in the wild, it is also native to Australia where it is known as Kangaroo Apple. It has also naturalised in New Caledonia, Hawaii, and in western USA. It is a relatively fast-growing and soft-wooded shrub which grows to a height of 2-3 metres, it has dark green distinctive asymmetric leaves, and a purple-white blossom very similar to that of the potato. The plants tend to grow for a few years and then die, but are quite effective at self-seeding.

The ripe berries of poroporo were traditionally eaten as a food in Aotearoa and Australia, and poroporo was planted by Māori around pā and in plantations for the value of their fruit, which was popular with children. When ripe these are yellow-orange in colour and have a mild acidic taste, not dissimilar from the cape gooseberry (Physalis peruviana). Several references to the eating of berries either cooked or uncooked by Māori exist in early New Zealand literature. Early settlers stewed the berries and made them into pies and jam, calling them Māori gooseberries and bullabull. However, like unripe tomatoes and potatoes, unripe green berries or the leaves can cause digestive upset when ingested in quantity, and should therefore only be used topically.

Apart from being desirable for its ripe fruit, poroporo is used as a natural medicine, particularly the leaves, which can help in the treatment of a wide range of skin conditions. The leaves and other aerial parts can be prepared as a lotion, poultice, ointment or cream and applied to inflammatory skin conditions. It makes an excellent alternative to fresh chickweed for contact dermatitis (eczema), and also conditions such as psoriasis, or any other situation in which itchiness is a feature.

Many reports appear in the writings of early European migrants to New Zealand, about poroporo leaves being heated or infused into oil, then applied to bring much-needed symptomatic relief to those suffering from "the itch"⁽¹⁾. With the importation of sheep, cattle and chickens came also plenty of parasitical insects, leading to another use found for topical poroporo applications.

The botanically related Solanum dulcamara (bittersweet), is also popular in Western herbal medicine for the treatment of scrophulous skin conditions, and is approved by the German Commission E for topical use as a supportive treatment in eczema. Application of another Solanaceae family plant, Solanum nigrum (black nightshade), improved the skin in a mouse model of atopic dermatitis, effects associated with reduced expression of various inflammatory cytokines (2 Hong 2020). Steroidal alkaloids such as solasonine and solasodine are key compounds found in both Solanum dulcamara and Solanum nigrum as well as in S aviculare and S laciniatum, and are almost certainly contributory to the anti-pruritic, anti-inflammatory and wound healing properties shown by poroporo and other Solanum spp^{(3, 4)}.

With the seasons changing and spring and summer allergens and pollens arriving, we will experience the usual increase in atopic dermatitis and other inflammatory and pruritic skin complaints as a result of warmer temperatures and more outdoor living. From allergic reactions to insect bites or infestations, saddle sores or sunburn, poroporo can be an effective phytomedicine for a wide range of common dermatological complaints where inflammation, soreness or itchiness are featured. It is therefore a good one for herbal practitioners in Aotearoa to have on hand during the coming months.

References:

1. Riley Murdoch, 1994. Maori Healing and Herbal. New Zealand Ethnobotanical Sourcebook. pub Viking Sevenseas NZ Ltd, Paraparaumu, New Zealand. ISBN 0 85467 095 5.
2. Hong, S. et al, Solanum nigrum Linne improves DNCB-induced atopic dermatitis-like skin disease in BALB/c mice. Molecular medicine reports, 2020; 22(4), 2878-2886.
3. Piana M, et al. Topical anti-inflammatory activity of Solanum corymbiflorum leaves. J Ethnopharmacol. 2016;179:16-21.