Though my time with this project, garlic as a holistic treatment for seborrheic dermatitis has continued to come up from time to time. To be fair, when my own issues were at their peak, I did end-up experimenting with this in several different forms (garlic oil capsules, whole gloves, crushed gloves, topical applications, enteric-coated capsules), but personally, had never seen any real benefit from any of these approaches.
On the surface, the theory and thinking behind the usage of garlic seems quite straightforward. Seborrheic dermatitis is known to respond to anti-fungal therapy (both topical and systemic) and garlic has well known natural anti-fungal properties. Hence, it’s easy to make the jump (garlic -> anti-fungal -> seborrheic dermatitis).
Despite my own lack of progress with any of the above-mentioned uses of garlic, it seemed worthwhile to return to the investigation. At the very least, it would be interesting to hear why some online sources have not only promoted this approach but why they had the success they did.
Review outcome: Garlic clearly has a number of benefits for human health; many of which are well matched to the primary features of seborrheic dermatitis. And while there isn’t enough evidence to support its use specifically for the treatment of seborrheic dermatitis, regular consumption may still tip the scales in our favor.
What is known about garlic’s anti-fungal properties
Let’s start the investigation with some review of the significance of garlic’s antifungal properties:
- One of the most studied components of garlic is allicin  and preliminary studies have shown its ability to suppress certain fungi is comparative to well know azole drugs (these are some of the most commonly used antifungal agents) 
- Diallyl trisulfide is another less known component of garlic, but it has also shown significant antifungal activity 
- The large majority of these studies are “in vitro”, meaning the effect were shown in a lab setting and “in vivo” (real-life) studies are limited 
Possible complementary benefits of garlic in relation to the key features of seborrheic dermatitis
Even if we disregard the possibility for garlic’s antifungal properties to be effective enough to control the symptoms of seborrheic dermatitis, it’s possible that some of its other properties may be of use.
Decades of research on garlic, have shown that garlic possesses a variety of beneficial properties in addition to its antimicrobial properties. These include:
- Improved lipid profile and beneficial impact on cardiovascular disease 
- Various routes of immune system modulation (cytokine secretion, immunoglobulin production, phagocytosis, and macrophage activation) 
- Enhanced regulation of blood sugar 
- Antioxidant potential (more so for aged garlic – see notes) 
- Reduction in inflammation 
And considering that some of the core documented features of seborrheic dermatitis include an abnormal immune response, increased levels of free radicals, and a run-away inflammatory response; garlic seems to be well-positioned to at-least assist on one of these fronts.
Historical references to garlic in the treatment of dandruff
Looking through the medical texts, it was interesting to find that garlic actually has quite a long history of use in the treatment of dandruff:
- Arabian herbalists use garlic for the treatment of dandruff 
- European botanists of the 1500s had commonly prescribed garlic 
Granted these references aren’t really that much better than anecdotal (there have been some strange remedies used throughout history that wouldn’t even be considered today), but it’s pleasing to see that it seems to have been utilized.
The merits of topical application
The majority of the article has primarily focused on the possible effects of garlic when it’s eaten. But some have alluded to the application of various garlic extracts directly to the skin to increase the antifungal effect against the Malassezia on the skin surface.
Plus the fact that there are some studies that do indeed demonstrate that topical application of carefully prepared solutions can be beneficial for the treatment of a number of skin conditions  makes it seem like a worthy idea.
But while this may seem like a plausible idea at first, if given some additional thought the idea doesn’t seem as attractive.
Seborrheic dermatitis and dandruff are confined to sebum rich areas of skin. These areas are typically also significantly more sensitive and the condition itself makes them even more so.
And unfortunately, garlic isn’t very mild. The topical application of homemade preparations has been associated with contact dermatitis , chemical burns  and even second degree burns . So for most of us, it’s probably best to avoid too much experimentation on this front.
Theorizing a possible mode of action for some individuals
Going back to those reported success cases mentioned in the beginning, what characteristics of garlic would best explain the symptom relief best? What makes garlic unique? After all, many known extracts and plants have significantly greater antioxidant potential, anti-inflammatory properties, and even immune modulation effects.
If having to select the two most unique to garlic, it would have to be it’s antifungal (helping to reduce Malassezia activity on the skin surface) and lipid-lowering properties (potentially influencing the sebum lipid profile).
These are probably the two properties of garlic that continued to fuel the research interest in the plant and also are significantly more pronounced in garlic (when compared to a large number of other candidates).
However, speculating further is unlikely to be of much use. There are far too many factors and unknowns. Plus, there really isn’t any more research specific to the effect of garlic on seborrheic dermatitis that I could dig up in.
- Other plants from the same family (such as onions, leeks, shallots, etc) also contain allicin in varying concentrations and some level of substitution may be possible
- Shampoo fortified with microwave dried garlic powder was shown to be effective at controlling the growth of various Malassezia strains 
- Black garlic (also known as aged garlic) extracts have a big following in Eastern medicine and the production process appears to amplify many of its beneficial characteristic [15, 16]
- There is such a thing a too much of a good thing and negative effects have been reported when the dosage is abnormally high [17, 7]
- Some extraction methods promote the conversion of Allicin to Ajoene, which could be a more useful antifungal agent in the fight against malassezia [18, 19]
- Due to the instability of the sulfur rich compound in garlic, extracting shelf stable actives for the production of supplements difficult to achieve and puts doubt on their effectiveness 
Garlic has a wide variety of documented benefits on human health and many of them seem to be suited to be of assistance in the primary features of seborrheic dermatitis. Unfortunately, while anecdotal evidence exists, there really isn’t any data in the medical literature to either confirm or deny its use for the treatment of seborrheic dermatitis.
One this is clear, the benefits of garlic seem to greatly outweigh any potential shortcomings. And integrating garlic into your regular diet is likely to be favorable in the long term.
For those with personal experience (success stories or cautionary tales), would love to hear your input in the comments section below.