Meghan Markle probably can't use her favourite $15 miracle cure-all right now.

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Prince Harry and Meghan Markle are on the first day of their Australian royal tour – where they’ll be combatting all our favourite pests, like mossies and spiders.

Which is why it’s so unfortunate that the Duchess of Sussex probably cannot use her favourite cure-all right now.

The 37-year-old has previously described how tea tree oil is her travel must-have. But the potent essential oil isn’t recommended for pregnant women – a group we just learned Meghan is apart of.

“The one thing that I cannot live without when I’m travelling is a small container of tea tree oil,” Meghan told Allure last year.

“It’s not the most glamorous thing, but if you get a cut, a mosquito bite, a small breakout, no matter what it is, it’s my little cure-all. It’s inexpensive, it’s small enough to carry on, and I bring it with me all the time.”

Meghan and Prince Harry will just have to keep a citronella candle close by. Image: Getty.

However, Meghan would most likely have been modifying the way she used her favourite product these past few months. It's recommended that women in their first trimester of pregnancy do not apply essential oils directly onto their skin and instead dilute and use sparingly, if at all.

In the second and third trimester, it's recommended that women talk to their GPs about using essential oils such as tea tree oil.

And that's because it's potent stuff. Distilled from the Australian plant Melaleuca alternifolia, tea tree oil possesses strong antimicrobial and anti-inflammatory properties. Several studies have suggested its use for treating acne, seborrheic dermatitis, chronic gingivitis and even to accelerate the wound-healing process.

It's relatively affordable - a 50mL bottle of Thursday Plantation Tea Tree Oil, for example, generally retails at around $15.99.

And for us non-pregnant folk? Dermatologist Janet Prystowsky explained to Huffington Post, any essential oil - including tea tree - should be used with caution by anyone with sensitive skin, especially those with a tendency for eczema.

"It is probably best to buy tea tree oil already in the dilution needed rather than mixing it yourself," Dr. Prystowsky said.

Although, there are some DIY techniques that can help make it more gentle for the face.

"Add a couple drops to aloe vera gel, and then apply the gel to pimples or blemishes. You can also add a couple teaspoons of tea tree oil to raw organic honey."