Diploma in Aromatic Science

This is a unique opportunity to get deep insight into Aromatic Science!

Four certification courses, four single classes, a new essential oil database, four international tutors, a cohort of fellow students with the same dedication as yours to discover the full journey of an essential oil – from the plant, through the production process and into our bodies.

Your tutors are Robert Tisserand, a global expert in the field of essential oils with 50+ years of experience, Petra Ratajc, PhD, biochemist and aromatherapy educator who spearheaded scientific aromatherapy in Slovenia, Joy E. Bowles, PhD, Australian essential oil science communicator and specialist famous for her deep dives into research rabbit holes, and Hana Tisserand, the heart of the Tisserand Institute with 15 years of adult education under her belt. Together they form a powerhouse of knowledge that is guaranteed to show you how to create the solid evidence-base your essential oil practice deserves.

Spend the eight months learning all there is to know about essential oils, and connecting to your fellow essential oil enthusiasts from all over the world in a dedicated group, just for the Diploma Program.

What You Get in the Diploma Program

FOUR FULL COURSES – 30 weeks of instruction in two terms 
The Aromatic Science Diploma consists of 4 of our certification courses – Beyond the Bottle 2e (updated in 2023), Aromatic Chemistry, Essential Oil Kinetics Masterclass and Essential Oil Safety Masterclass 2e.

You will also get access to Essential Calculation, Oxidation and Shelf-life, The Joy of Research and Biosynthesis single classes.

As a part of the diploma you will have full access to our essential oil profile database – the most up-to date and evidence based resource on essential oil uses and applications.

We are here to make sure you succeed on your journey – with regular live student groups and an extra forum just for the Diploma cohort.

You will be able to consult your final project work with the tutors before you submit it for grading, and the project options are designed to help translate your knowledge into practical application – with a research poster, scientific presentation, or a publishable article.

On top of the eight months of instruction, you will get plenty of extra time to develop and work on your finals.

Including student forums, live lessons and Q&A sessions, printable materials and guidance.

Course Schedule

There are two terms in 2023:

Term one  May 2nd – August 15th

Term two August 22nd – December 30th

There are 26 weeks of classes, spread over 7 months, after which there is time for finals and assessments. The 4 single classes are scheduled on separate weeks.


Classes run once per week, and most are 50 minutes, plus Q&A. Beyond the Bottle with Dr. Ratajc lessons will be live, and recorded for you to watch later. Other course lessons are pre-recorded. For the pre-recorded courses there are live Q&A sessions once every 2-3 weeks.

Study time

Students should allow about 3 hours per week for study, or more if interested.

Course Content

Look at the “What courses you will be taking?” section below for each course – detailed class content can be found through the link in the description.


There is a quiz at the end of each class, and an exam at the end of each course. There are separate quizzes for single classes. There will also be practical project work, which will be assessed at the end of the full program.


All of our training courses are accredited as continuing education by the National Association for Holistic Aromatherapy (NAHA). Most relevant professional organizations will accept our courses for CE credits, and we’re happy to assist with the paperwork.

If at any point you find you are struggling

We are here to help you. On top of our usual student support that you know from other courses, the Diploma program comes with a dedicated support group with monthly meetings with our team. We want you to succeed!

What courses will you be taking? 

Beyond the Bottle: Understanding Essential Oils 2e (update in 2023)

Instructor: Petra Ratajc, PhD

Should you grow your own lavender for home distillation? How do you really know what you’re getting when buying essential oils? How do you know if an essential oil has been adulterated, or has oxidized? And how can you make sensible, sustainable choices? This is the complete journey from cultivation to cracking the lid on the bottle in your hand, with highlights on production, sustainability and quality control. NEW lesson added and all lessons updated with most recent research!  More here

Biosynthesis: The Origins of Essential Oils (single class)

Instructor: Petra Ratajc, PhD

An “essential oil” is the liquid that is distilled (or expressed) from a plant. This class is a dive into what happens before we harvest aromatic plants to create essential oils. Dr Ratajc looks at why and how plants create volatile compounds that form their essential oils, and explains what determines both the similarities and the variations in different oils. More here

Aromatic Chemistry

Instructor: E Joy Bowles, PhD

In this course, Dr. Joy Bowles, scientist and aromatherapist, will take you down the wonderful rabbit hole of organic chemistry – all the way down to the molecular level – and illustrate in understandable terms how and why essential oils are able to deliver therapeutic effects. Dr. Joy Bowles as she draws on her unique experience as a scientist and aromatherapist to unlock the fascinating mysteries of essential oil chemistry. More here.

The Joy of Research (single class)

Instructor: E Joy Bowles, PhD

This class will equip you with enough understanding of how research is conducted, reported and critiqued, to assess the quality and relevance of the document you are reading. Some research studies are better than others and some are more trustworthy and more applicable to the use of essential oils. Dr Joy will empower you to become the detective – building your case, evaluating the evidence, and then coming to a conclusion. More here

Essential Oil Safety Masterclass, 2nd Edition

Instructor: Robert Tisserand

This eight-part online course will show you how to evaluate the risks against the benefits of essential oils, and make informed decisions about safety. You will delve into the science, and the reasoning behind safety guidelines. Whatever your level of knowledge, this certification masterclass will enable you to confidently and safely use essential oils according to current evidence and best practices. New and updated lessons in 2022! More here

Essential Calculation (single class)

Instructor: Hana Tisserand

You love essential oils, and you got hooked into aromatherapy – but nobody told you there will be math. And looking at all the ratios, percentages, milliliters, ounces, drops, maximum dilutions and charts can seem daunting. But it doesn’t have to be! Join Hana Tisserand as she guides you through calculations and conversions with ease, giving you simple tools and making sure you get it, so you will never again have to ask: “How many drops is that?” More here.

Essential Oil Kinetics Masterclass

Instructor: Petra Ratajc, PhD

Over six weekly lessons, Dr. Petra Ratajc will introduce you to pharmacokinetics – the journey that essential oil constituents take as they move through your body – and what this means for effective application. We’ll compare psychological and pharmacological mechanisms, look at the blood-brain barrier, and the fascinating “nose-to-brain” route. Finally, we’ll discuss appropriate dose, dilution, delivery system, and mode of application, based on everything we have learned. More here

Oxidation and Shelf Life (single class)

Instructor: Robert Tisserand

This single class delves into the issues of oxidation and the proper storage of essential oils. Robert Tisserand explains how to best protect your oils from oxidation, what to do once they have oxidized, and how oxidation impacts safety. Included is a printable handout with the shelf lives of most commonly used essential oils. More here.

Meet your tutors

Robert Tisserand

Author | Speaker | Founder of Tisserand Institute

Robert is one of the world’s leading experts in aromatherapy with over 40 years of experience. He is a speaker, educator, author, and consultant on the science and benefits of essential oils and their safe and effective application. Robert has inspired audiences in the UK, USA, Canada, Australia, Brazil, Czech Republic, China, Hong Kong, Taiwan, Korea and Japan on topics ranging from the therapeutic foundations of essential oils to examinations on essential oils and the skin.

Robert wrote one of the first books to bring awareness to aromatherapy in 1977, The Art of Aromatherapy, and is a co-author of Essential Oil Safety (2nd Edition, 2014), a book that sets industry standards for the safe use of essential oils.

Hana Tisserand

Chief of Operations | Educator | Course Moderator

Hana is our captain of operations and communications. She hails from Prague, and brings a strong background in French and English translation and interpretation that’s proven essential for our global student base. Being raised in a family of doctors and nurses had primed her for a specialization in medical translation, which she counts alongside her experience working with politicians, authors, and educators. She has been working with Robert Tisserand for six years.

Hana supervises our staff, manages our teaching platform, organizes courses, hosts webinars, commissions blog posts, oversees the creation of social content, writes our newsletters, and is our go-to IT technician. Somehow, she finds time to write her own blog posts, too.

Dr. Petra Ratajc, PhD

Biologist | Researcher | Educator

Petra refers to herself as an ‘aromatic plants enthusiast’ and has a post-graduate degree in Biological and Biotechnical Sciences from the University of Ljubljana. Her PhD extends from fieldwork to molecular research in the quality, safety and efficacy of aromatic herbs and their essential oils.

Petra specializes in medicinal and aromatic plants, secondary plant metabolites, pharmacognosy and pharmacology specifically focused on plant volatile constituents. Visit her myth-busting plant biology blog, The PhytoVolatilome.

Dr. Joy Bowles; PhD, BSc Hons

Educator | Research Expert |  International Speaker

In 1991, Dr. Joy Bowles wrote the first course in essential oil chemistry in Australia. Her book The Chemistry of Aromatherapeutic Oils, published in 2003, is a standard text for aromatherapy courses around the world. This work moves step-by-step at the molecular level through 89 essential oils, along with techniques for applying the benefits of aromatherapy to the various body systems.

For her PhD, awarded in 2007, Dr. Joy investigated the effects of essential oils on cognitive function in dementia. After several years in primary healthcare, she’s returned to the field of essential oil chemistry, training practitioners on the evidence-based therapeutic effects of essential oils. Helping people understand the chemistry and pharmacology of essential oils is one of her life’s passions.

When You Complete the Diploma


Your diploma will be signed by Robert Tisserand, Petra Ratajc, Joy Bowles and Dr. Kandace Knudsen, our education director. The Tisserand Institute has been setting the global standard for evidence based high quality essential oil education for many years. Your diploma will be a proof of your knowledge and expertise. 

A detailed transcript of your course curriculum, including contact hour counts, as further proof of your expertise and continuing education.

The Tisserand Institute is proud to have a global body of learners, and during the months of the program you will be able to create new contacts for knowledge sharing as well as inspiring collaborations. We will also feature you in a directory of diploma graduates. 

Why a diploma and not just individual courses?

From the inception of the Tisserand Institute, we wanted to create a modular, stackable form of essential oil education. This means that you can pick and choose individual courses according to your needs, and at the same time build a bigger credential.

Now, you can build something bigger from scratch. Similar to a university program, you can step beyond individual classes and courses, and become a part of a diploma group that journeys through them all together. Plus, we will be assessing competencies, and not just knowledge.

Cohort-based learning

Cohort-based learning is a collaborative learning style in which a group of individuals advance through an educational program together. Here are some of the benefits of cohort learning:

Support: Cohort learning connects you to the support of peers and faculty.

Structure: Because you advance through a program with others, cohort learning provides structure in the form of set due dates (weekly, monthly, etc.) and discussion forums.

Collaboration: Especially in an online environment, a cohort learning model facilitates social interaction and collaboration with your peers. This can enhance your learning experience and sense of community as you progress through an online program.

Perspective: A cohort learning model expands your perspectives. This is a unique benefit of cohort vs. on-demand learning; in the latter, your perspectives are the only ones available.

What previous students say about these classes:

The extraordinary expertise of R. Tisserand in EO. Explanations are clear, based on facts and clinical facts. Wonderful courses. ~ Laure Mattia
Thank you for such a wonderful and informative class! I have learned an abundance of wonderful information to not only help me to help others, but also to be able share my newly attained knowledge to help others better understand EO safety. I’m hoping for more of these in the future as I expand my knowledge of Aromatherapy! Thank you again! Blessings to all! ~ Lisa Macy

I wanted to thank you so much for this class! It was wonderfully organized and I looked forward to it every week. I really appreciate all your efforts to bring essential oil safety awareness to everyone. I am constantly referring to your book in my store and recommend it to all of my students. Thank you, thank you, thank you! I am really looking forward to future classes! ~ Natalie Hajdu-Voakes

I enjoyed the way Hana and Robert interact to make sure the material is understood. ~ Debra Gildernew

I want to thank you for this course. I feel so confident having your institute as my education platform. I’m a beginner but with your amazing education, it won’t be long before I’m a pro!

The prompt response to our questions is fantastic. The presentations each week are very educational, they address my concerns about safety, and the overall format is brilliant!

I really enjoyed the course! Hope to take another in the future. Thank you both! ~ Carol Friberg

This is a rare opportunity to study with some of the world’s leading experts – don’t miss this chance! Let Robert Tisserand, Joy Bowles and Petra Ratajc guide you in getting the best essential oil education based on solid scientific research.

Ready to get started?


Will there be notes for me to review?
Yes. Each lesson comes with printable handouts of the slides used in the lesson, and additional lesson notes. These are sent to you before each lesson and are for you to keep and refer to at any time.
I am a certified aromatherapist. Will I learn anything new?
Many of our students have commented that our courses helped them grasp what they learned elsewhere in more detail, or complemented their previous education. Some of our students are lifelong learners, and some are teachers.
I am new to essential oils. Is this course for me?
We will let one of our previous students answer this one:

“The information presented is appropriate for all levels, and although I am just beginning my aromatherapy journey it all makes sense.”

Will there be assessments or exams? What kind?

Each weekly lesson is followed by a multiple choice quiz, and there is a summary test at the end of each course. Passing both the weekly quizzes and the final tests is a requirement for certification.

You will be given enough time to prepare for the test as well as three attempts to pass. 

Will I be able to ask questions?

Absolutely! In addition to the live Q&A sessions, you can post your questions in the dedicated student forums where the tutor and the TI team will address them. 

What if I cannot participate on a live session?

All of our live sessions are recorded and are posted on the learning platform within 24 hours so you can watch them, or rewatch as needed during the course. 

How long will I have access to the recordings?

You will have access to all the videos for at least four weeks after the last lesson (see course description for clarification as this changes for individual courses). All the printable materials (notes, handouts, charts, etc.) are of course yours to keep for reference forever.

Do you offer continuing education credits?

Because we have students from all over the world and of many professions we are not able to offer credits for specific organizations – there are simply too many. However, we issue a confirmation of CE hours gained on the course that you can apply with your professional organization and will be happy to assist with any additional documentation.

At the moment, we are an Approved Continuing Education Provider with NAHA. 

What if I fall behind or cannot attend classes?
We have found that running classes on specific dates works best to help you finish a program. You join a class of students, and learn along with them. Many students help each other with queries, and of course our tutors are there too. That said, if you miss a few classes you should be still able to comfortably jump right back in and if you do fall behind you can request extra time. Of course this cannot be indefinite, but we do our best to help you get your certificate.