What Is a Clinical Trial? A Plain-Language Guide for People With Hidradenitis Suppurativa

If you live with hidradenitis suppurativa (HS), also called acne inversa, you may have heard that new treatments are being studied — or a doctor may have mentioned a clinical trial. That can raise a lot of questions. What is a clinical trial, really? Is it safe? Would you be a “test subject”? Do you have to take part if you look into one?

This guide answers those questions in plain language. Learning about trials creates no obligation to join one. Understanding how they work simply helps you have a clearer, calmer conversation with a study team or your own doctor. This article is for general education only and is not medical advice; decisions about clinical trial participation should always be made together with qualified healthcare professionals.

What a clinical trial is

A clinical trial is a carefully planned research study that tests a medical question in people — for example, whether a new medicine reduces HS flaresFlare: A period of acute worsening in a chronic condition. In Acne Inversa, a flare may be triggered by stress, hormonal changes, friction, or other factors and can manifest as new nodules, abscesses, or increased pain.FlareA period of acute worsening in a chronic condition. In Acne Inversa, a flare may be triggered by stress, hormonal changes, friction, or other factors and can manifest as new nodules, abscesses, or increased pain.Read more in the glossary, or whether a procedure heals better than another. It follows a written plan (the “protocol”), is reviewed by an independent ethics committee, and is run under rules designed to protect the people who take part.

The key idea to hold onto is this: a clinical trial is research, not guaranteed treatment. Its purpose is to find reliable answers that can help future patients — and, sometimes but not always, the people in the study.

Why clinical trials are conducted

Before a treatment can be recommended or approved, someone has to show that it actually works and that its benefits outweigh its risks. Clinical trials are how that evidence is built, step by step. They answer questions like:

• Does this treatment reduce painful nodulesNodule: A firm, palpable lump deep in tissue. Nodules can be painful and may progress to abscesses. They are among the typical early signs of Acne Inversa.NoduleA firm, palpable lump deep in tissue. Nodules can be painful and may progress to abscesses. They are among the typical early signs of Acne Inversa.Read more in the glossary, abscessesAbscess: An inflamed cavity or swelling containing pus or fluid. In hidradenitis suppurativa, abscesses can form as part of the inflammatory disease process and do not automatically mean that a bacterial infection is present. Secondary bacterial infection can occur and may require separate medical assessment. In Acne Inversa, abscesses occur mainly in the armpits, groin, and other skin folds.AbscessAn inflamed cavity or swelling containing pus or fluid. In hidradenitis suppurativa, abscesses can form as part of the inflammatory disease process and do not automatically mean that a bacterial infection is present. Secondary bacterial infection can occur and may require separate medical assessment. In Acne Inversa, abscesses occur mainly in the armpits, groin, and other skin folds.Read more in the glossary or draining tunnelsDraining Tunnel: A sinus tract or fistula actively leaking fluid (serous, purulent, or blood-tinged) to the surface. Draining tunnels carry the heaviest weight in modern HS severity scores because they signal long-standing, structurally damaged disease.Draining TunnelA sinus tract or fistula actively leaking fluid (serous, purulent, or blood-tinged) to the surface. Draining tunnels carry the heaviest weight in modern HS severity scores because they signal long-standing, structurally damaged disease.Read more in the glossary?
• How often do side effects happen, and how serious are they?
• What dose works best?
• Does it work better than what is already available?

Every approved HS treatment that exists today — including the biologicBiologic: A class of medications derived from living cells that target specific components of the inflammatory process. For Acne Inversa, biologics such as adalimumab and secukinumab are used when other treatments are insufficient.BiologicA class of medications derived from living cells that target specific components of the inflammatory process. For Acne Inversa, biologics such as adalimumab and secukinumab are used when other treatments are insufficient.Read more in the glossary medicines now prescribed for moderate-to-severe disease — reached patients because clinical trials tested it first. Whether any given treatment is suitable and how well it works can vary from person to person.

Interventional versus observational studies

There are two broad kinds of study, and the difference matters:

• Interventional (treatment) studies assign participants to receive something — a medicine, a procedure or another intervention — as part of the research. The researchers are actively testing that intervention.
• Observational studies collect information without assigning a study treatment. Researchers observe and record what happens with people’s usual care, for instance to understand how HS changes over time.

The Trial Finder on this site lets you filter for either type, because what participation involves is quite different between them.

The phases of a clinical trial

Medicines are usually tested in a sequence of phases, each answering a bigger question:

• Phase 1 — a small group, mainly checking safety, dosing and how the body handles the treatment.
• Phase 2 — a larger group, looking for early signs that it works while continuing to watch safety.
• Phase 3 — a large study, often in many countries, comparing the treatment against a placeboPlacebo: An inactive substance, usually identical in appearance to the real drug, used in clinical trials to control for the meaningful placebo response in Acne Inversa.PlaceboAn inactive substance, usually identical in appearance to the real drug, used in clinical trials to control for the meaningful placebo response in Acne Inversa.Read more in the glossary or standard care. This is usually the evidence regulators rely on for approval. The HS biologics were established through Phase 3 programmes.
• Phase 4 — studies conducted after a medicine is approved, to follow long-term safety and real-world use.

Knowing the phase gives you a rough sense of how much is already known about a treatment.

Screening, inclusion and exclusion criteria

Every study defines who can take part. Inclusion criteria describe who is eligible (for example, a certain age range or a certain severity of HS). Exclusion criteria describe who cannot take part (for example, certain other conditions or medicines). These exist to keep participants safe and to make the results meaningful.

Before you can join, there is usually a screening visit: the team reviews your history, may run tests, and checks the criteria in detail. It is completely normal to be interested and then learn you do not meet the criteria. That is not a personal judgement — it is how studies protect participants and produce reliable answers.

Informed consent

You cannot be enrolled in a trial without informed consent. The team must explain the study in a way you understand — its purpose, what you would do, the possible risks and benefits, and your rights — and give you time and space to ask questions. You then decide freely whether to sign.

Consent is ongoing, not a one-time signature. You can ask questions at any point, and you can withdraw your consent later.

Randomisation, control groups, placebos and blinding

Several terms describe how trials stay fair and reliable:

• Randomisation means a computer, not a person, decides which group you are placed in. This prevents bias in who gets which treatment.
• A control group is the comparison group — people who receive a placebo, standard care or an existing treatment — so researchers can tell whether the new treatment made the difference.
• A placebo is a dummy treatment with no active medicine. Not every trial uses one, and in serious conditions a placebo is often given on top of standard care rather than instead of it.
• Blinding means participants (and sometimes the team) do not know who is in which group, because expectations can influence how symptoms are judged. Safety rules always allow the team to “unblind” quickly if a medical situation requires it.

Study visits, questionnaires and symptom diaries

Taking part usually means visits to a study centre on a schedule. Depending on the study, participants may be asked to have physical examinations, blood tests, or photographs of affected areas, and to complete patient-reported questionnaires or a symptom diary — for example, rating pain or counting lesions over time. These measurements are how the study tracks whether the treatment is helping.

Potential benefits

For some people, potential benefits include close monitoring by a specialist team, access to a treatment being studied, and the sense of contributing to knowledge that may help others with HS. But it is important to be honest: a benefit is possible, not promised. An investigational treatment may not provide a direct benefit, and you might be in the comparison group.

Potential risks and burdens

Risks and burdens are real and worth weighing. An investigational treatment may have side effects that are not yet fully understood. Participation takes time — travel, appointments, tests — and some procedures, such as medical photography of sensitive areas, can feel uncomfortable. There may be uncertainty about which treatment you are receiving. A good study team will discuss all of this openly before you decide.

Research versus standard medical care

It helps to keep the two apart. Standard care is the treatment your doctor provides to help you as an individual. Research is designed to answer a question for future patients, using a fixed protocol that everyone follows. A trial may feel similar to normal care, but its first purpose is knowledge, and its rules are stricter. Importantly, taking part should never replace the care you need — participants should not stop or change existing treatment without discussing it with qualified healthcare professionals and the study team.

Can you leave a trial, and what happens when it ends?

Yes — you can leave at any time, for any reason, without affecting your normal care. When a trial ends, the data is analysed and the results are written up. Results are increasingly published in public registries such as ClinicalTrials.gov and the EU Clinical Trials Information System, and summaries may be shared with participants. Approval by regulators, if it happens at all, is a separate later step — trial completion does not automatically mean a treatment becomes available.

Questions to ask before considering participation

If you are thinking about a study, these are reasonable things to ask a study team:

• What is the purpose, and what is being tested?
• Is there a placebo or comparison group, and how is treatment assigned?
• How long does it last, and how many visits are involved?
• What are the known risks, burdens and possible benefits?
• What happens to my current HS treatment, and who do I call if things get worse?
• How is my data protected, and will I be told the results?

You do not have to remember all of this. Our downloadable questions checklist collects them in one place to take to an appointment.

Where to go next

If you would like to see what modern HS treatments were built on, read how clinical trials changed HS treatment. If you are weighing whether to contact a centre, what taking part may be like walks through the journey step by step. And when you are ready, you can explore open HS studies in Germany or return to the clinical trials hub.