There are two health conditions that are known to drastically increase the chance of being affected by seborrheic dermatitis. And investigating the nervous system dysfunctions in these conditions uncovers some interesting clues further highlighting its potential role in seborrheic dermatitis symptoms.
Relationship Between Parkinson’s and Seborrheic Dermatitis
While the rate of seborrheic dermatitis in general population is estimated at roughly 3%, in individuals suffering from Parkinson’s disease this figure rises closer to the 50% mark .
Because of this striking relationship, seborrheic dermatitis is often discussed and mentioned in the literature examining Parkinson’s disease. For example, in a 2017 paper, the authors classified seborrheic dermatitis as a “premotor feature of Parkinson’s disease referable to dysregulation of the autonomic nervous system” .
To put this relationship in context it may make sense to first review Parkinson’s disease. While an in-depth review is outside the scope of this work, some of the most important features of the condition include:
- A common neurodegenerative disorder
- Can be genetic, but more frequently it is idiopathic (can suddenly arise)
- No definitive treatment exists
- Tremor, stiffness, and loss of balance are the most prevalent symptoms
Possibly a more concise way to summarize the condition is that it is a myriad of symptoms that arise from the bodies inability to properly coordinate nervous system activity.
And two specific features of the Parkinson’s appear to be most relevant to the high rate of seborrheic dermatitis seen among those affected:
A repeating theme that we’ve seen in much of the evidence discussed in this chapter so far.
Additional Clues from Autonomic Nervous System Issues Seen in AIDS
The connection between AIDS and seborrheic dermatitis has already been previously mentioned in this book, but let’s review it once again in the context of the nervous system.
Out of all health conditions, HIV AIDS appears to have the strongest influence on the likelihood of the individual developing seborrheic dermatitis (3% in the general population versus upwards of 34%-83% in AIDS ).
One way to look at this connection is that AIDS has a disastrous impact on immune function, allowing the most common suspect of seborrheic dermatitis, the malassezia yeast, to proliferate freely and wreak havoc on the skin surface. In this line of thought, the immune system and its ability to properly deal with malassezia yeasts are at the heart of the resulting skin symptoms.
However, another way to look at this connection is to consider the impact of AIDS on the autonomic nervous system. And a quick review of the literature reveals the following:
- Autonomic nervous system dysfunction is common amongst individuals infected with HIV [6, 7]
- Damage of the autonomic nerve fiber is a hallmark of HIV and occurs early in the course of the infection 
- A possible reason for HIV to promote sympathetic bias is to improve its survival rate by changing the balance of the TH-1/TH-2 immune response (the former being considered more pro-inflammatory and the later more anti-inflammatory) 
In-line with this reasoning, it’s possible that the role of autonomic imbalance and it’s effect on both sebum production  and sweat output  leads to a dis-balanced skin micro flora; while the weakened immune system that favors the TH-1 response (inflammation) simply increase the magnitude of seborrheic dermatitis symptoms experienced.
Improving autonomic balance through cardiovascular exercise
Interestingly, one of the most straightforward methods to reduce the impact of HIVs effect on the autonomic immune function is through improvement of cardiovascular fitness .
This section examined the frequent occurrence of seborrheic dermatitis among individuals affected by Parkinson’s and AIDS.
Key points include:
- Seborrheic dermatitis is estimated to affect as much as 50% of individuals suffering from Parkinson’s and 34-83% of individuals with AIDS
- Parkinson’s is classified as a neurodegenerative disorder and loss of neural control over sebum and sweat production is common
- Evidence suggests that HIV also influences the central nervous system; promoting sympathetic bias which increases system levels of inflammation, and destabilizes sebum/sweat production
- Research speculate that the destabilized sebum/sweat production could be directly related to the high incidence rate of seborrheic dermatitis seen