Which of these are you trying to tell apart?
Nine conditions overlap in this space, and they overlap almost completely on symptoms. Each page below takes one confusable pair and says what actually separates them, which of the two can be investigated, and what nobody has settled yet.
Why this is so hard to sort out
The short answer
These conditions are not different flavours of the same thing. Some are defined by a test result, some by a symptom pattern after other causes were excluded, and some by criteria specialists still dispute. Comparing them symptom by symptom fails because the symptoms are the part that matches. What differs is what kind of claim each label is.Find your pair
- Is it IBS or a food intolerance?Three things get called a food reaction: immune allergy, enzyme deficiency, and fermentation. They need different tests, and one common panel is not one.
- Is it IBS or MCAS?IBS is a gut diagnosis of exclusion. MCAS is a systemic one. If your symptoms leave the gut, that is the observation that matters most here.
- Is it IBS or SIBO?IBS is a diagnosis of exclusion. SIBO is a test result. That difference explains why people carry both labels, and why the two breath tests disagree.
- Is it long COVID or POTS?One of these has a bedside test that produces a number. The other does not. That is the most useful thing to know before you spend money investigating either.
- Is it MCAS or a food intolerance?Three different things get called a food reaction and one word covers all of them. Which one you have decides which test means anything.
- Is it MCAS or histamine intolerance?One is cells releasing mediators. The other is difficulty handling a compound in food. They feel similar, and one set of criteria is still disputed.
- Is it MCAS or long COVID?Both can begin after an infection and both produce gut symptoms. Timing is the discriminator most people reach for, and it is weaker than it looks.
- Is it MCAS or mold illness?The least settled pair we cover. One has criteria specialists dispute. The other has no accepted diagnostic definition in mainstream medicine at all.
- Is it MCAS or POTS?These two plus hypermobility form a well documented cluster. Co-occurrence is expected, which means asking which one you have is frequently the wrong question.
- Is it SIBO or a food intolerance?Both produce symptoms after eating, and the timing overlaps more than most pages admit. The useful split is fermentation versus enzyme versus immune.
- Is it SIBO or candida?One of these has a test that specialists argue about. The other has essentially no accepted test at all. That difference matters more than the symptom lists.
- Is it SIBO or histamine intolerance?Gut bacteria can produce histamine. That is a real mechanism and a routinely overstated one: shared mechanism is not the same as one causing the other.
- Is it SIBO or MCAS?The figures linking these two come from specialist clinics, where everyone was referred for being complicated. That inflates any overlap you compute.
- Why the diagnostics here are contestedNot a gap in your reading. Specialists genuinely disagree about the tests, the criteria and in some cases whether a condition exists as described.
Not seeing your combination? We only write a pair page where there is enough real patient discussion to say something specific about it, rather than filling in every possible permutation. How we decide that.
Common questions
- Can I have more than one of these at once?
- For most of these pairs, yes. Several are recognised as co-occurring more often than chance predicts. That is why we frame these pages as telling two things apart rather than as choosing between them.
- Why can symptoms not tell these conditions apart?
- Because the symptom profiles overlap almost completely. The main clinical guideline in this area states that no single symptom can be specifically attributed to the one condition that does have a test, which sets a hard ceiling on symptom-based reasoning.
- Which of these can actually be tested for?
- Fewer than you would hope. Bacterial overgrowth has a breath test with published thresholds that specialists actively argue about. Postural tachycardia has a structured standing test that produces a number. Mast cell activation has two competing criteria sets that disagree about who qualifies. Gut candida and chronic mold illness have no test endorsed as diagnostic by a major medical body.
- Where should I start if I am not sure which pair applies to me?
- With whichever part of your picture has a test capable of producing a result. A structured standing test is inexpensive and gives a number. Knowing which gases a breath test can physically measure matters before you pay for one. Both are answerable questions, unlike which of two contested labels fits you.